【Objective】To investigate the effect of the ER stress on the process of nonalcoholic fatty liver disease which is induced by methionine-choline deficient diet.【Methods】C57/BL mice were randomly divided into 8 groups（n = 10），group 1-4 was given normal diet，5-8 group was given MCD diet. Then took one group from both normal diet and MCD diet in the 2nd，4th， 6th，8th week，recorded each group′s body weight and liver weight. The liver fibrosis and inflammation in mice were analyzed by his? topathological staining and NAS. The expressions of endoplasmic reticulum stress markers such as p-PERK，p-eIF2α，CHOP were detected by Western Blot and real time fluorescent quantitative PCR（q-PCR）.【Results】①The ALT and AST in serum，TG and TC in liver tissue were both higher in MCD group，the same as NAS；②The expressions of PERK，eIF2α，CHOP were significantly high? er than the normal diet group，while the GADD34 expression was lower. What′s more，as time went by，the difference was more obvi? ous；3. There was a significant correlation between the ERS index and NAS score in MCD group.【Conclusion】The liver damage and inflammatory response was lifted gradually in the mice fed with MCD diet. The ER stress may take an important role in this process.