Objectives: This study was designed to investigate the effects of Yongdamsagantang on the polycystic ovary(PCO) induced by estradiol valerate(EV) in rats. Methods: After administrating Yongdamsagan-tang to PCO induced rats, we measured the weight of body, ovaries, adrenal glands, and uterus of rats. The observation through naked eye and histopathological observation of ovaries were evaluated. Also, the number of follicle and corpora lutea and content of androstenedione(ADD) and total estrogen were evaluated. The expressions of nerve growth factor(NGF) and corticotropin releasing factor(CRF) were analyzed by immunohistochemistry. The breeding rate and number of implantation with normal male rats were evaluated. Results: - The weight(mg) of ovaries in YST treated group($73.8{pm}7.6$) was significantly increased(p<0.001) compared with control group($54.3{pm}4.5$). - The number of mature follicles in YST treated group($7.3{pm}2.4$) was significantly increased(p<0.01) compared with control group($3.5{pm}1.2$). - The number of atretic follicles in YST treated group($9.0{pm}1.5$) was significantly decreased(p<0.01) compared with control group($13.4{pm}3.8$). - The number of cystic follicles in YST treated group($3.1{pm}1.1$) was significantly decreased(p<0.01) compared with control group($6.0{pm}2.0$). - The number of corpora lutea in YST treated group($3.8{pm}2.1$) was significantly increased(p<0.001) compared with control group($0.3{pm}0.7$). - The expression of NGF-immunoreactive cells in the ovarian granulosa cells in YST treated group was lesser observed than control group. - The expression of NGF-immunoreactive cells in the adrenal cortex in YST treated group was lesser observed than control group. - The breeding rate in YST treated group(100 %) was significantly increased (p<0.05) compared with control group(50 %). - The number of implantation in YST treated group($6.4{pm}4.7$) was significantly increased(p<0.05) compared with control group($1.4{pm}2.6$). Conclusions: We concluded that Yongdamsagan-tang activates the maturation of follicles, normal ovulation, breeding rate and number of implantation. Therefore, this may be effective for the treatment of anovulation, amenorrhea and sterility of PCOS patients.