Objective To analyse the expression and clinical significance of 12 kinds of microRNAs (miR) in patients with ovarian cancer using public gene expression databases. Methods The microRNA expression data were screened in dataset GSE14407 and TCGA database, then 12 kinds of microRNAs were obtained including miR-10B, miR-1244, miR-622, miR-21, miR-503, Let-7D, miR-155, miR-30C, miR-17, miR-101-1, miR-186 and miR-770. The expression data of these 12 kinds of microRNAs were compared and identified to find the differential ones between normal tissue and tumors. Data of 505 ovary cancer patients were divided into two groups by age, tumor grade, clinical stage, disease location, tumor residual and microRNA expression. Kaplan-Meier survival analysis and Cox multivariate analysis were used to compare the overall survival of ovary cancer patients between two groups. Results Compared with ovary cancer, the expression levels of Let-7D and miR-101-1 were higher, but the expression levels of miR-155 and miR-770 were decreased, in adjacent tissue of ovary tumor (P<0.05). The Kaplan-Meier survival analysis result showed that lower survival rates were found in patients with age≥59 years, clinical stage (Ⅲ+Ⅳ) and lower Let-7D expression (P<0.05). The multivariate Cox regression analysis showed that the decreased expression level of Let-7D was the independent risk factor for the prognosis of ovarian cancer. Conclusion The expression of Let-7D is correlated with the prognosis of ovarian cancer, which is the independent biomarker to predict prognosis of ovarian cancer.