Purpose <p>Polycystic ovary syndrome (PCOS) severely affects fertility and quality of life in women of reproductive age. Research has shown that microRNAs (miRNAs) may play a role in the development of PCOS. This study focused on the clinical significance and potential function of miR-18a-3p in PCOS, aiming to find a new molecular marker for screening and progression prediction in PCOS.</p> Methods <p>The expression of miR-18a-3p was detected by real-time quantitative PCR. The function of miR-18a-3p on the phenotype of human ovarian granulosa cells (KGN) was assessed by cell counting kit-8 assay and apoptosis assay. The downstream mechanisms by which miR-18a-3p were explored by bioinformatics methods and dual-luciferase reporter assay. The effect of CITED2 expression on the function of miR-18a-3p in KGN cells was further examined.</p> Results <p>miR-18a-3p was downregulated in the serum and follicular fluid of PCOS patients and showed clinical significance in screening for PCOS. Low levels of miR-18a-3p were associated with the level of HOMA-IR, LH, Testosterone, and AMH in PCOS patients. In KGN cells, the inhibition of miR-18a-3p expression promoted apoptosis and suppressed cell viability, whereas overexpression of miR-18a-3p exhibited the opposite effect. miR-18a-3p targeted and negatively modulated CITED2 to exert its effect in KGN cells. Furthermore, miR-18a-3p modulated the PI3K/AKT signaling pathway mediated by CITED2.</p> Conclusions <p>Downregulation of miR-18a-3p demonstrates potential as a diagnostic marker for PCOS. miR-18a-3p affected the phenotype of KGN cells and modulated the PI3K/AKT signaling pathway through CITED2.</p>