Relationship between the methylation status of the RASSF2A gene promoter and endometriosis-associated ovarian cancer (EAOC) was explored. Between January 2013 and January 2016, tissue samples were collected from 30 patients diagnosed with ovarian endometriosis cyst (EC group), 30 patients diagnosed with ovarian endometrial adenocarcinoma (OEA group) and 30 patients diagnosed with ovarian clear cell carcinoma (OCC group). Additionally, 30 cases of normal endometrium tissues were collected for the control group. The methylation status of the RASSF2A promoter was evaluated by combined bisulfite restriction enzyme analysis (COBRA). RT-PCR was used to detect the expression level of RASSF2A mRNA in tissues. Relationship between methylation status and RASSF2A mRNA expression level and the patient age, tumor clinical stage, tumor grading and pathological type were analyzed. Results showed that in the OEA and OCC groups, the methylation degrees of the RASSF2A promoter were obviously higher than that of the other two groups. The expression level of RASSF2A mRNA in the OEA and OCC groups was lower than that of the other two groups. The methylation degree of the RASSF2A promoter was related to clinical staging and grading. No relationship between the methylation degree of the RASSF2A promoter and patients age and the pathological type of the tissue was detected. We concluded that the methylation status of the RASSF2A gene promoter could be considered an excellent indicator for early detection of ovarian cancers.