The roles of the androgen receptor (AR) in female fertility and ovarian function remain largely unknown. Here we report on the generation of female mice lacking AR (AR(-/-)) and the resulting influences on the reproductive system. Female AR(-/-) mice appear normal but show longer estrous cycles and reduced fertility. The ovaries from sexually mature AR(-/-) females exhibited a marked reduction in the number of corpora lutea. After superovulation treatment, the AR(-/-) ovaries produced fewer oocytes and also showed fewer corpora lutea. During the periovulatory period, an intensive granulosa apoptosis event occurs in the AR(-/-) preovulatory follicles, concurrent with the down-regulation of p21 and progesterone receptor expression. Furthermore, the defective conformation of the cumulus cell-oocyte complex from the AR(-/-) females implies a lower fertilization capability of the AR(-/-) oocytes. In addition to insufficient progesterone production, the diminished endometrial growth in uteri in response to exogenous gonadotropins indicates that AR(-/-) females exhibit a luteal phase defect. Taken together, these data provide in vivo evidence showing that AR plays an important role in female reproduction.