Abstract: Objective To measure the expression of heat shock protein 70 （HSP70） in mice embryos with the stimulation of chronic mild anticipatory stress (CUMS) to female Kunming mice. Methods Three hundreds female Kunming mice were stressed by 9 chronic mild unpredictable stress factors for 28 days and then divided into three groups of mild, moderate and severe stress. PMSG/hCG was measured to assess the induction of superovulation, and ovarian response and embryo development potential were observed. The expression of HSP70 in 2-cell embryos and day 4 embryos was detected by immunofluorescence and real time polymerase chain reaction (RT-PCR). Results After 28 d CUMS stimulation, the rate of mice in mild, moderate and severe stress were 50%, 32% and 18%，respectively. In the mild stress group, ovarian response and oocyte development potential were similar to those of control, while HSP70 expression of the embryos was significantly higher (P<0.05). In the severe stress group, ovarian response and oocyte development potential were significantly decreased compared with the control group (P<0.05), while HSP70 expression was similar to that of control. Conclusion HSP70 overexpression observed in the embryos may be related to its proteetive effect against chronic unpredictable stress.