Objective To investigate the effects of vitamin D on inflammatory state in rats with polycystic ovary syndrome (PCOS). Methods Twenty-four immature female SD rats(three weeks-old, 57±6g)were randomly divided into control, PCOS, and PCOS+VD group, 8 rats in each group. In the last 2 groups, letrozole (1mg/kg·d, in 0.5% carboxymethyl cellulose) and high-fat diet were administered intragastrically, meanwhile, control rats were intragastric with solvent. Twenty-eight consecutive days later, the PCOS+VD group was intragastric with 200IU/kg·d VD daily, the control group and PCOS groups were intragastric with corn oil at the same volume. ELISA was performed to detect serum 25-(OH)D, T, LH, FSH, IL-6, IL-17, TNF-α, CRP, FINS, and IL-6, IL-17, TNF-α, CRP proteins of ovarian tissue were measured by western blot analysis. HE staining was carried out to observe the ovarial morphological changes. Results Serum 25-(OH)D level in PCOS rats decreased (P<0.05), while serum T, LH, FPG, FINS level increased(P<0.05), and the level of IL-6, IL-17, TNF-α and CRP significantly increased in both serum and ovarian tissue compared with control rats(P<0.05). The estrous cycle of the PCOS rats was disturbed, and the ovary presented a large number of cystic follicles, with sparse corpus luteum. Serum 25-(OH)D in PCOS+VD rats was significantly higher than that in PCOS rats. However, the level of T, LH, IL-6, IL-1,7 TNF-α, CRP, FPG and FIN was reverse, and the estrous cycle was relatively regular with fewer cystic follicles and more corpus lutea. Conclusion VD can reduce the content of inflammatory factors and improve the inflammatory state in PCOS rats.