Background: To investigate the effects of tannic acid (TA) use on ovarian folliculogenesis, p53 expression, and serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T) levels in rats with polycystic ovary syndrome (PCOS) model. Materials and Methods:A total of 18 Wistar female rats were used and divided into 3 experimental groups. Group 1 (G1, control), group 2 (G2, PCOS), group 3 (G3, PCOS+TA). Rats were induced with letrozole for 21 days to form a PCOS model. After 21 days, TA (40 mg/kg) was given by gavage for 10 days and the rats were sacrificed on the 10 th day. PCOS formation was evaluated by daily estrous cycle follow-up. Hematoxylin & eosin and p53 immunohistochemical staining was performed on ovaries. Serum FSH, LH, and T levels were determined by ELISA. Data were analyzed with the One-Way ANOVA test and Kruskal-Wallis H test. P<0.05 was considered statistically significant. Results:The number of cystic follicles was significantly increased in the PCOS group compared to the TA treatment group (p<0.05). The number of primary follicles was significantly increased in the TA treatment group (p<0.001). No significant change was observed in the number of primordial, secondary, and Graaf follicles between the experimental groups. A significant increase in LH and T was observed in the PCOS group (p<0.05). The increase in LH has significantly decreased TA administered rats (p<0.05). Although it was not significant, serum FSH level was increased in the PCOS+TA group. No immunoreactivity was detected in p53 staining in experimental groups. Conclusion:TA can decrease cystic follicle formation and increase primary follicle formation in PCOS. Also, it can regulate the hormonal expression of serum LH, FSH, and T in PCOS-modeled rats.