Abstract: Objective: To investigate the promoter hypermethylation status of tumor suppressor Ras association domain family 1A (RASSF 1A) gene in ovarian cancer,peritoneal fluid and the value of diagnosis of ovarian cancer.Methods: The promoter methylation status of the promoter region of RASSF 1A was analyzed by methylation specific-PCR in forty-two malignant ovarian tumor tissues and ascites (or peritoneal fluid),eleven normal ovarian tissues and ninteen benign ovarian tumor tissues.Results: The promoter methylation rate of RASSF 1A in ovarian cancer was 38.1% while in benign tissues was 0.The rate of promoter hypermethylation of RASSF 1A in ovarian cancer and noncancer tissues showed significant correlation (P<0.01).The frequency of promoter methylation of RASSF 1A was correlated with operation-pathology stage and lymph node metastasis.There was statistically significant difference.Hypermethylation of RASSF 1A gene happened more often in tumors in stage Ⅲ and Ⅳ 54.2% than that in stage Ⅰand Ⅱ 16.6% (P<0.05).The frequency of promoter methylation of RASSF 1A was significantly higher in the patients with positive lymph node metastasis 56.5% than those without lymph node metastasis 15.8% (P<0.01).The frequency of methylation of promoter region in RASSF 1A gene was significantly higher in the patients with positive ascites or peritoneal liquid 74.1% than in those negative ascites or peritoneal liquid 33.3% (P<0.01).Conclusions: There was significant frequency promoter methylation of RASSF 1A in ovarian cancer.Detection of aberrant RASSF 1A methylation may serve as an early diagnostic and prognostic marker.