MicroRNAs (miRNAs) can serve as biomarkers in human cancer. To determine the clinical value of urinary miRNAs for ovarian serous adenocarcinoma, we collected urine samples from 39 ovarian serous adenocarcinoma patients, 26 patients with benign gynecological disease and 30 healthy controls. The miRNA microarray data showed that only miR-30a-5p was upregulated and 37 miRNAs were downregulated in the urine samples of ovarian serous adenocarcinoma patients, when compared to healthy controls, which was confirmed after conducting quantitative PCR. The upregulation of urinary miR-30a-5p was closely associated with early stage of ovarian serous adenocarcinoma as well as lymphatic metastasis. Receiver operator characteristic (ROC) analysis demonstrated the potential use of urinary miR-30a-5p as a diagnostic marker for ovarian serous adenocarcinoma. Furthermore, a lower urine level of miR-30a-5p was found in 20 gastric cancer and 20 colon carcinoma patients when compared to ovarian serous adenocarcinoma, suggesting that the upregulation of urinary miR-30a-5p may be specific for ovarian serous adenocarcinoma. miR-30a-5p was also upregulated in ovarian serous adenocarcinoma tissues and cell lines, while urinary miR-30a-5p from ovarian cancer patients was notably reduced following the surgical removal of ovarian serous adenocarcinoma, suggesting that urinary miR-30a-5p was derived from the ovarian serous adenocarcinoma tissue. Notably, miR-30a-5p was concentrated with exosomes from the ovarian cancer cell supernatant or urine from ovarian serous adenocarcinoma patients, supporting a pathway for excretion into the urine. The results also showed that the knockdown of miR-30a-5p significantly inhibited the proliferation and migration of ovarian cancer cells. In summary, to the best of our knowledge, the present study provided the first evidence of increased miR-30a-5p in the urine of ovarian serous adeno-carcinoma patients, while the inhibition of miR-30a-5p suppressed the malignant phenotypes of ovarian cancer in vitro. Therefore, miR-30a-5p serves as a promising diagnostic and therapeutic target for ovarian serous adenocarcinoma.