Abstract: Objective: To study the significance of endoplasmic reticulum stress in hepatocytes apoptosis.Methods: The BALB/c mouse primary hepatocytes were isolated by two-step in situ liver perfusion,and then induced apoptosis with 4 μmol/L thapsigargin.siRNA against caspase-12 were synthesized chemically,then transfected into mouse primary hepatocytes by liposomes.Efficacy of caspase-12-siRNA inhibition was analyzed with RT-PCR and Western blot;viability of hepatocyte following apoptosis was evaluated with MTT.Results: The inhibition of caspase-12 mRNA and procaspase-12 expression were 86.22% and 50.04% respectively with 200 nmol/L siRNA (P<0.01).Contrasted with apoptotic hepatocytes,the cell activity analyzed with MTT increased by 51.65% (P<0.05).Conclusions: The mouse primary hepatocyte apoptosis can be reduced when endoplasmic reticulum stress-induced caspase-12 is inhibited.Endoplasmic reticulum stress plays an important role in hepatocyte apoptosis.