Objective To explore the effects of low-dose mifepristone on human granulosa cells and the molecular mechanism of its inhibiting or delaying ovulation. Methods Phase contrast microscopy and electron microscopy were conducted to observe the morphological and biochemical change of granulosa cells exposed to various doses of mifepristone for 24 hours (the final concentrations of mifepristone were respectively 2.5μmol/L, 5μmol/L and 10μmol/L, Non-mifepristone as the control group). Immunocytochemistry was performed to detect the protein expressions of Bcl-2 and Bax in granulosa cells exposed to various doses of mifepristone for 24 hours. The mRNA levels of Bcl-2 and Bax in granulosa cells were detected by RT-PCR. Results Granulosa cells treated with various doses of mifepristone presented typical morphological characteristics of apoptosis such as condensation of chromatin and cytosolic, and shrink of cells. The expression of Bcl-2 protein might be down-regulated, while the expression of Bax might be up-regulated by mifepristone. The histological score (HSCORE) of Bcl-2 protein in granulosa cells, which were incubated with various doses of mifepristone (2.5μmol/L, 5μmol/L, 10μmol/L) for 24 hours, were respectively 2.15±0.16,1.88±0.13 and 1.64±0.16 respectively，Compared with the HSCORE of the control group (2.51±0.16), the difference was significant （EM>P/EM><0.001）. Compared with the control group (1.50±0.16), there was singificant difference in the expression of Bax protein (1.85±0.10, 2.00±0.18 and 2.29±0.20) （EM>P/EM>