diff --git a/main.py b/main.py
index ad41fd2..d63bd76 100644
--- a/main.py
+++ b/main.py
@@ -11,6 +11,7 @@
 from parallel_utils import map_layers_to_multi_gpus, get_lowest_occupied_gpu
 import torch.nn as nn
 from quantize.omniquant import omniquant
+from quantize.gptq import gptq
 from tqdm import tqdm
 import utils
 from pathlib import Path
@@ -218,6 +219,7 @@ def main():
     parser.add_argument("--aug_loss", default=False, action="store_true", help="calculate additional loss with same input")
     parser.add_argument("--symmetric",default=False, action="store_true", help="symmetric quantization")
     parser.add_argument("--disable_zero_point",default=False, action="store_true", help="quantization without zero_point")
+    parser.add_argument("--gptq", default=False, action="store_true", help="use gptq for further compensation")
     parser.add_argument("--a_dynamic_method", type=str, default="per_token", choices=["per_token"])
     parser.add_argument("--w_dynamic_method", type=str, default="per_channel", choices=["per_channel"])
     parser.add_argument("--limit", type=int, default=-1)
@@ -351,6 +353,11 @@ def main():
             logger,
         )
         logger.info(time.time() - tick)
+        if args.gptq:
+            tick = time.time()
+            with torch.no_grad():
+                gptq(lm, args, dataloader, logger)
+            logger.info(time.time() - tick)
     if args.save_dir:
         # delete omni parameters
         for name, module in lm.model.named_modules():
diff --git a/quantize/gptq.py b/quantize/gptq.py
new file mode 100755
index 0000000..86319c1
--- /dev/null
+++ b/quantize/gptq.py
@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# Copyright [2024-01-23] <sxc19@mails.tsinghua.edu.cn, Xingchen Song>
+
+import torch
+import math
+
+from auto_gptq.quantization.gptq import GPTQ
+from auto_gptq.modeling._utils import find_layers
+
+from quantize.quantizer import FixedScaleQuantizer
+from quantize.int_linear import QuantLinear
+from quantize.utils import set_quant_state, smooth_and_quant_inplace
+
+
+def gptq(lm, args, dataloader, logger):
+    logger.info("Starting GPTQ...")
+
+    # 1. move embedding layer and first layer to target device
+    model = lm.model
+    dev = lm.device
+    logger.info("model.device: {}".format(dev))
+    use_cache = model.config.use_cache
+    model.config.use_cache = False
+    is_llama = False
+    # TODO(xcsong): support other archs
+    if "llama" in args.net.lower():
+        is_llama = True
+        layers = model.model.layers
+        model.model.embed_tokens = model.model.embed_tokens.to(dev)
+        model.model.norm = model.model.norm.to(dev)
+        layers_block_name = "model.layers"
+        inside_layer_modules = [
+            ["self_attn.k_proj", "self_attn.v_proj", "self_attn.q_proj"],
+            ["self_attn.o_proj"],
+            ["mlp.up_proj", "mlp.gate_proj"],
+            ["mlp.down_proj"]
+        ]
+    else:
+        raise ValueError("Only support for Llama-2 now")
+    layers[0] = layers[0].to(dev)
+
+    # 2. catch the first layer input
+    dtype = next(iter(model.parameters())).dtype
+    logger.info("model.dtype: {}".format(dtype))
+    inps = torch.zeros(
+        (args.nsamples, lm.seqlen, model.config.hidden_size),
+        dtype=dtype, device=dev
+    )
+    outs = torch.zeros_like(inps)
+    cache = {"i": 0, 'attention_mask': None}
+
+    class Catcher(torch.nn.Module):
+        def __init__(self, module):
+            super().__init__()
+            self.module = module
+            self.is_llama = False
+
+        def forward(self, inp, **kwargs):
+            inps[cache["i"]] = inp
+            cache["i"] += 1
+            cache["attention_mask"] = kwargs["attention_mask"]
+            if self.is_llama:
+                cache["position_ids"] = kwargs["position_ids"]
+            raise ValueError
+
+    layers[0] = Catcher(layers[0])
+    layers[0].is_llama = is_llama
+
+    for batch in dataloader:
+        if cache["i"] >= args.nsamples:
+            break
+        try:
+            model(batch[0].to(dev))
+        except ValueError:
+            pass
+
+    # 3. move embedding layer and first layer to cpu
+    layers[0] = layers[0].module
+    layers[0] = layers[0].cpu()
+    if "llama" in args.net.lower():
+        model.model.embed_tokens = model.model.embed_tokens.cpu()
+        model.model.norm = model.model.norm.cpu()
+    else:
+        raise ValueError("Only support for Llama-2 now")
+    torch.cuda.empty_cache()
+
+    # 4. get additional inputs (mask, pos, ..., etc)
+    attention_mask = cache["attention_mask"]
+    if is_llama:
+        position_ids = cache["position_ids"]
+    else:
+        position_ids = None
+
+    # 5. start gptq quantization
+    quantizers = {}
+    for i in range(len(layers)):
+        logger.info(f"=== Start quantize layer {i} with GPTQ ===")
+        layer = layers[i].to(dev)
+
+        # 5.1 get layers which should be quantized
+        full = find_layers(layer, layers=[QuantLinear])
+        for names in inside_layer_modules:
+            # NOTE(xcsong): type(subset[name]) == QuantLinear
+            #   i.e. subset["self_attn.k_proj"] = QuantLinear(**someargs)
+            #               type(gptq[name]) == GPTQ
+            #   i.e. gptq["self_attn.k_proj"] = GPTQ(subset["self_attn.k_proj"])  # noqa
+            subset = {n: full[n] for n in names if n in full}
+            gptq = {}
+            # 5.1.1 init gptq
+            for name in subset:
+                gptq[name] = GPTQ(subset[name])
+                # NOTE(xcsong): Overwrite GPTQ().quantizer, use fixed scale
+                #   and zero obtained from omniquant's quantizer
+                _ = subset[name].weight_quantizer(subset[name].weight)
+                subset[name].weight_quantizer.register_scales_and_zeros()
+                scale = subset[name].weight_quantizer.scales
+                zero = subset[name].weight_quantizer.zeros \
+                    if subset[name].weight_quantizer.zeros is not None \
+                    else torch.zeros_like(scale)
+                gptq[name].quantizer = FixedScaleQuantizer(
+                    scale=scale, zero=zero,
+                    **args.weight_quant_params,
+                    shape=subset[name].weight.shape
+                )
+
+            # 5.1.2 init gptq.H
+            # NOTE(xcsong): Overwrite GPTQ().add_batch(), since
+            #   1. type(gptq[name].layer) is QuantLinear, not nn.Linear,
+            #       making it incompatible with the original implementation.
+            #   2. We might consider utilizing fake quantized activations
+            #       for the calculation of H.
+            def add_batch(name):
+                def tmp(_, inp, out):
+                    # apply fake_quant to actiavtion
+                    inp = subset[name].act_quantizer(inp[0].data)
+                    if len(inp.shape) == 2:
+                        inp = inp.unsqueeze(0)
+                    batch = inp.shape[0]
+                    if isinstance(gptq[name].layer, QuantLinear):
+                        if len(inp.shape) == 3:
+                            inp = inp.reshape((-1, inp.shape[-1]))
+                        inp = inp.t()
+                    else:
+                        raise NotImplementedError()
+                    gptq[name].H *= gptq[name].nsamples / (gptq[name].nsamples + batch)
+                    gptq[name].nsamples += batch
+                    inp = math.sqrt(2 / gptq[name].nsamples) * inp.float()
+                    gptq[name].H += inp.matmul(inp.t())
+                return tmp
+
+            handles = []
+            for name in subset:
+                set_quant_state(subset[name], weight_quant=False,
+                                act_quant=False)
+                subset[name].use_temporary_parameter = False
+                handles.append(subset[name].register_forward_hook(
+                    add_batch(name)))
+            for j in range(args.nsamples):
+                layer(inps[j].unsqueeze(0),
+                      attention_mask=attention_mask,
+                      position_ids=position_ids)[0]
+            for h in handles:
+                h.remove()
+
+            # 5.1.3 do gptq-algorithm and update weight in-place
+            for name in subset:
+                logger.info(f'Quantize {name} in layer {i + 1}/{len(layers)}')
+                scale, zero, g_idx = gptq[name].fasterquant(
+                    blocksize=128,  # same as gptq
+                    percdamp=0.01,  # same as gptq, always choose 1% of the average diagonal value  # noqa
+                    group_size=-1 if args.group_size is None else args.group_size,  # group = None means per-channel  # noqa
+                    actorder=False,
+                    static_groups=False
+                )
+                quantizers[f'{layers_block_name}.{i}.{name}'] = (
+                    gptq[name].quantizer.cpu(), scale.cpu(),
+                    zero.cpu(), g_idx.cpu()
+                )
+                gptq[name].free()
+                torch.cuda.empty_cache()
+
+        # 5.2 quantize weight optimized by gptq
+        # NOTE(xcsong): After GPTQ quantization, we do
+        #   online fake_quantize for activation (via set_quant_state)
+        #       and
+        #   offline in-place fake_quantize for weights (via smooth_and_quant_inplace)
+        layer.half()
+        set_quant_state(layer, weight_quant=False, act_quant=True)
+        prev_let, prev_gptq = args.let, args.gptq
+        args.let, args.gptq = False, False
+        smooth_and_quant_inplace(layer, args)
+        args.let, args.gptq = prev_let, prev_gptq
+
+        # 5.3 get output of current layer, treat it as input for next layer
+        for j in range(args.nsamples):
+            outs[j] = layer(inps[j].unsqueeze(0),
+                            attention_mask=attention_mask,
+                            position_ids=position_ids)[0]
+        inps, outs = outs, inps
+        layers[i] = layer.cpu()
+        torch.cuda.empty_cache()
+
+    model.config.use_cache = use_cache
diff --git a/quantize/quantizer.py b/quantize/quantizer.py
index 49cdc1a..53c44e0 100644
--- a/quantize/quantizer.py
+++ b/quantize/quantizer.py
@@ -10,8 +10,6 @@
 CLIPMIN = 1e-5
 
 
-
-
 def round_ste(x: torch.Tensor):
     """
     Implement Straight-Through Estimator for rounding operation.
@@ -163,3 +161,58 @@ def register_scales_and_zeros(self):
         self.register_buffer('zeros', self.round_zero_point)
         del self.scale
         del self.round_zero_point
+
+
+class FixedScaleQuantizer(UniformAffineQuantizer):
+    def __init__(
+        self,
+        scale,
+        zero,
+        n_bits: int = 8,
+        symmetric: bool = False,
+        per_channel_axes=[],
+        metric="minmax",
+        dynamic=False,
+        dynamic_method="per_cluster",
+        group_size=None,
+        shape=None,
+        lwc=False,
+        disable_zero_point=False
+    ):
+        UniformAffineQuantizer.__init__(
+            self,
+            n_bits,
+            symmetric,
+            per_channel_axes,
+            metric,
+            dynamic,
+            dynamic_method,
+            group_size,
+            shape,
+            lwc,
+            disable_zero_point
+        )
+        # Init scale & zero
+        self.scale = scale
+        self.zero = zero
+
+    # NOTE(xcsong): Overwrite AutoGptqQuantizer.find_params() since there is
+    #   no need to re-compute scale and zero
+    def find_params(self, x, weight=False):
+        pass
+
+    # NOTE(xcsong): Overwrite AutoGptqQuantizer.ready() since there is
+    #   no need to re-compute scale and zero
+    def ready(self):
+        return True
+
+    # NOTE(xcsong): Overwrite AutoGptqQuantizer.quantize() since we have a
+    #   slightly different quantization process
+    def quantize(self, x):
+        if self.n_bits >= 16:
+            return x
+        if self.metric == "fix0to1":
+            return x.mul_(2**self.n_bits-1).round_().div_(2**self.n_bits-1)
+
+        x_dequant = self.fake_quant(x, self.scale, self.zero)
+        return x_dequant
diff --git a/quantize/utils.py b/quantize/utils.py
index e2b339d..ae74e88 100644
--- a/quantize/utils.py
+++ b/quantize/utils.py
@@ -111,10 +111,13 @@ def smooth_and_quant_inplace(model, args):
                             model.out_smooth_scale, model.out_smooth_shift)
         smooth_q_k_inplace(model.self_attn.q_proj, model.self_attn.k_proj,
                             model.qkt_smooth_scale)
-    for name, module in model.named_modules():
-        if isinstance(module, QuantLinear):
-            module.weight = module.weight_quantizer(module.weight)
-            module.use_temporary_parameter=False
+    if not args.gptq:
+        # NOTE(xcsong): Instead of fake_quantized weights,
+        #   We need original weights to calculate errors for GPTQ
+        for _, module in model.named_modules():
+            if isinstance(module, QuantLinear):
+                module.weight = module.weight_quantizer(module.weight)
+                module.use_temporary_parameter = False
 
 def set_quant_state(self, weight_quant: bool = False, act_quant: bool = False):
     # setting weight quantization here does not affect actual forward pass