OBJECTIVE: Ovarian endometriosis seriously affects the quality of life of females, and long non-coding RNA lncRNA urothelial carcinoma-associated 1 (UCA1) plays pivotal roles in the pathogenesis of various ovarian diseases. However, the involvement of lncRNA UCA1 in ovarian endometriosis remains unknown to date. Therefore, the present study aims to study the role of UCA1 in ovarian endometriosis. METHODS: A total of 98 patients with ovarian endometriosis and 28 healthy females were included. The expression of lncRNA UCA1 in ectopic and eutopic endometrium tissues of ovarian endometriosis patients and controls was detected using qRT-PCR. A ROC curve analysis was performed to evaluate the diagnostic values of serum lncRNA UCA1 for ovarian endometriosis. Patients were followed up for 2 years after discharge, and the recurrence of ovarian endometriosis was recorded. RESULTS: The expression level of lncRNA UCA1 was significantly higher in ectopic endometrium tissues than in paired eutopic endometrium tissues for most of the patients. The serum lncRNA UCA1 level showed no significant correlations with either patients' age or living habits. After the treatment, the serum lncRNA UCA1 level increased, and serum levels of lncRNA UCA1 on the day of discharge were significantly lower in patients with recurrence than those in patients without recurrence. Conclusion: The downregulation of lncRNA UCA1 is involved in the pathogenesis of ovarian endometriosis and may serve as a promising diagnostic and prognostic biomarker for the disease.