MicroRNAs (miRNAs or miRs)-9 expression was reported to be upregulated in the follicular fluid of patients with polycystic ovary syndrome (PCOS). However, whether miR-9 affects ovarian dysfunction of PCOS and the related mechanisms are still unclear. Here we detected miR-9 and vitamin D receptor (VDR) expression in women with PCOS and controls, and investigated whether miR-9 affects ovarian granulosa cells (GCs) proliferation and apoptosis by targeting VDR. We found increased miR-9 and decreased VDR in the blood and isolated ovarian GCs of women with PCOS compared with the controls. MiR-9 promoted GCs proliferation and inhibited GCs apoptosis in vitro, and these effects were attenuated by its target VDR. High concentrations of insulin upregulated miR-9 expression in GCs. In conclusion this study firstly proved miR-9 affects ovarian GCs proliferation and apoptosis through targeting VDR. MiR-9 might be a potential molecular target for improving the dysfunction of GCs in PCOS.