Objective: The study aimed to investigate expression of p53, p27 and Jun activation domain-binding protein 1 (Jab1) proteins in epithelial ovarian tumors and the values of these factors as discriminating markers for the transformation of borderline tumors to cancers. Methods: Forty-seven cases of paraffin-embedded tissues of epithelial ovarian tumors including 22 cases of benign ovarian tumors, nine cases of borderline tumors, and 16 cases of invasive cancers were used to evaluate expression of p53, p27 and Jab1 proteins by immunohistochemical methods. Results: p53 protein was expressed in 13.6% of the benign tumors, 44.4% of the borderline tumors and 62.5% of the malignant tumors and p27 protein was expressed in 95.5% of the benign tumors, 66.7% of the borderline tumors, and 37.5% of the malignant tumors. Expression of Jab1 protein was observed in 22.7% of the benign tumors, 77.8% of the borderline tumors and 62.5% of the malignant tumors. Expressions of p53, p27 and Jab1 proteins in malignant tumors were all higher than in benign tumors and the expression of p27 protein in malignant tumors was lower than in benign tumors (p < 0.05). Expression of Jab1 protein in borderline tumors was significantly higher than in benign tumors (p < 0.05). Conclusions: Expression of p53, p27 and Jab1 proteins can be used to discriminate between benign and malignant tumors in epithelial ovarian tumors.