Abstract: Objective : To investigate the expression of Tiam1(T lymphoma invasion and metastasis inducing protein 1) and Racl in human ovarian carcinomas and to explore the correlation between the expression of Tiaml and Racl and the malignant status,including histological types,clinical stage,pathological grade, and metastasis. Methods : Immunohistochemistry (SP method) and semiquantitative analysis were used to measure the expression of Tiaml and Racl in 52 cases of human ovarian carcinomas, 12 cases of human benign ovarian tumors and 14 cases of human normal ovaries. Results :Tiam1 and Rac1 protein was expressed in 80.77 % and 78.00 % of patients with human ovarian carcinoma s respectively, whose expression was higher than those in human benign ovarian tumors and human normal ovaries, suggesting that the difference reached statistical significance (P<0.05). There was no obvious difference in the expression of Tiaml and Racl among the histological types and years of age of human ovarian carcinomas. The positive expression of Tiaml and Racl in clinical stage Ⅲ and Ⅳ(87.18% and 89.74%), as well as with metastasis (90.63% and 96.87%), were higher than those in clinical stage Ⅰ and Ⅱ(61.53% and 46.15%),as well as with non-metastasis (65.00% and 50.00%). The staining intensity of Tiaml and Racl increased gradually with the decrease of the degree of differentiation and the positive expression rate for both Tiaml and Racl in pathological grade Ⅱ and Ⅲ were significantly higher than in pathological grade Ⅰ . Conclusion: The expression of Tiaml and Racl in human ovarian carcinomas is correlated with the clinical stage, the degree of differentiation and tumor metastasis. Tiam1/Rac1 signaling may play a positive role in tumor cell invasion and metastasis.