P>Objective To investigate the relationship between the expression of Bcl-2/Bax protein and follicular development and apoptosis. Methods Immunohistochemical technology was utilized to study the distribution and positive reaction intensity of apoptosis protein Bcl-2/Bax in 95 rat ovaries from different postnatal developmental days. Value of absorbance of Bcl-2/Bax positive reaction in ovary sections was measured by the computer image analysis system. Results Positive staining for Bcl-2/Bax existed in the oocytes of different class follicles from 0 dayold to 360 dayold rat ovaries. Bcl-2 positive reaction in health oocytes was stronger than Bax,whereas Bax positive reaction in degenerative oocytes was stronger than Bcl-2 The expression pattern of Bcl-2/Bax was different in follicular cells, in which Bcl-2 was positive reaction from the postnatal first 21days rat, negative reaction from 21 dayold to 150 dayold rat,and negative in health follicles and positive in atretic follicles from older rat than 180 dayold. Bax reaction in follicular cells was all negative from younger rat than 180 dayold and liked Bcl-2 from older rat than 180 dayold. Expression of Bcl-2/Bax in theca cells was similar to follicular cells. Expression of Bcl-2/Bax in corpora luteum was observed only from older rat than 180 dayold. Conclusion Bcl-2/Bax may play an