Abstract: Objective To observe the expression of glucose-regulated protein 78 （Grp78） and caspase-12 in hypoxic rat cardiomyocytes. Methods Neonatal rat cardiomyocytes were randomly divided into control group and hypoxia 0.25h,0.5h,1h,1.5h,2h,4h,8h,12h,16h,24h groups.Apoptosis was assayed by TUNEL.Expression of Grp78 and caspase-12 was detected by Western blot at different time points. Results Compared with the control group,the apoptotic index increased with hypoxia time,the expression of Grp78 increased at 0.25h after hypoxia and reached its peak at 1h.The expression of procaspase-12 protein in the hypoxic group increased at 0.5h and reached its peak at 2h after hypoxia.The expression of caspase-12 increased at 1h and reached its peak at 4h after hypoxia compared with the control group. Conclusion Hypoxia can induce ER stress response,and endoplasmic reticulum stress is involved in apoptosis of cardiomyocytes after hypoxia.