Objective: To investigate the expression patterns of DNA methyltransferase 3-like (DNMT3L) protein in malignant ovarian germ cell tumors and the underlying roles in the pathogenesis of germ cell tumors. Methods: A total of 59 cases of ovarian malignant germ cell tumors were collected which include 52 cases primitive germ cell tumors and 7 cases immature teratoma. Primitive germ cell tumors included 10 cases embryonal carcinoma, 22 cases yolk sac tumors, 13 cases dysgerminoma, and 7 cases mixed germ cell tumors; meanwhile 17 cases non-germ cell tumors were collected including 5 cases serous adenocarcinoma, 5 cases granulose cell tumors and 7 cases. SP immunohistochemistry was performed to detect the DNMT3L expression in tumor tissues. The relationship with clinical-pathologic features and histological categories were analyzed. Results: DNMT3L was mainly expressed in primitive germ cell tumors, with total 73.1% (38/52) positive expression, 85.7% (6/7) positive expression for mixed germ cell carcinoma, 84.6% (11/13) for dysgerminoma, 68.2% (15/22) for yolk sac tumors and 60% (6/10) for embryonal carcinoma. The expression of DNMT3L was negative in 7 cases immature teratoma and 17 cases non-germ cell carcinoma. DNMT3L-positive proportion correlated to FIGO staging and had no correlations to age and tumor size. Conclusion: DNMT3L has a high positive rate in the primitive germ cell tumor and has a good sensitivity and specificity for its diagnosis. The change of DNA methylation may play an important role in the process of ovarian primitive germ cell tumor.