Abstract: A modified aminoff method for the determination of serum sialic acid was applied to evaluate the diagnostic significance of this marker in ovarian cancer.138 gynecological patients were histopathologically confirmed and 100 healthy female donors were investigated.In 27 untreated ovarian cancer,the mean value of serum sialic acid（75.31±2.49mg%）was significantly higher than that in healthy adults（54.62±0.88mg%）.68mg% was adopted as a cut-off point between benign and malignant disorders.The positive rate in ovarian cancer was 77.78%,other gynecological malignant diseases,63.64%,and in benign gynecological tumors below one third.This method can be taken as a reference for the diagnosis and postoperative follow up of ovarian cancer. This determination,however.is a non-specific marker test for cancer,as it may be positive in about half of cases of pelvic inflammation and endometriosis.This must be in the interpretation of the results.