Polycystic ovary syndrome (PCOS) is a lifelong metabolic disorder and the most common cause of anovulatory infertility affecting women in reproductive age. Our recent study reported that apolipoprotein C3 (ApoC3) could be a potential diagnostic serum marker for metabolism disturbance in PCOS patients, but whether it is present in the ovaries and what role it plays has not yet been described.Aimed to investigate ApoC3 expression in ovary of PCOS, and to discuss its potential role in PCOS progression.ApoC3 expression in ovarian tissue samples from 12 PCOS patients along with 12 healthy controls were measured via immunohistochemistry (IHC). Also, the level of ApoC3 in follicular fluid from 14 patients diagnosed with PCOS and 13 control subjects were detected by ELISA. The expression and location of ApoC3 in ovaries of PCOS mice were tested weekly for three consecutive weeks during PCOS formation using real time PCR, Western Blot, IHC and immunofluorescence. The relation of ApoC3 and sex hormones was analyzed in mouse plasma. Additionally, the dynamic changes of ApoC3 level in ovaries of healthy mice during postnatal development was also investigated.ApoC3 levels in ovarian tissue and follicular fluid were significantly higher in PCOS patients than in controls (33.87 ± 4.11 vs. 27.71 ± 3.65, P < 0.01; 0.87 ± 0.09 vs. 0.51 ± 0.32 ng/mL, P < 0.05), respectively. In ovary, ApoC3 was found to be located in the cytoplasm of oocyte, and its expression gradually increased with PCOS progression (P < 0.05). Furthermore, correlation analysis showed that plasma ApoC3 level was closely associated with luteinizing hormone (r = 0.709, P = 0.001), testosterone (r = 0.627, P = 0.005) and anti-mullerian hormone (r = 0.680, P = 0.002) in PCOS mice. In addition, ApoC3 level in oocyte was physiologically increased and peaked on postnatal age 21 (P21), then decreased following P21 in healthy mice.We identified ApoC3 expression in oocyte. It may be involved in PCOS progression and possibly participate in the regulation of oocyte development.© 2023. BioMed Central Ltd., part of Springer Nature.