Objective: To investigate the expression of PAX-2 in endometrial hyperplastic lesions and type I endometrial carcinoma and its significance. Methods: Thirty-one cases of normal proliferative endometrium, 107 cases of benign hyperplastic endometrium, 58 cases of endometrioid intraepithelial neoplasia, and 76 cases of endometrioid carcinoma were enrolled. PAX-2 expression was detected by immunohistochemistry in the above mentioned lesions. Results: The normal expression rates of PAX-2 were gradually decreased in proliferative endometrium, benign hyperplastic endometrium, endometrioid intraepithelial neoplasia, and endometrioid carcinoma, with the rates of 77.4% (24/31), 7.5% (8/107), 1.7% (1/58), 0.0% (0/76), respectively. The difference was statistically significant (χ2=142.512, P<0.01). Conclusion: The loss of PAX-2 expression plays an important role in the carcinogenesis of endometrioid carcinoma and is an early event. The complete loss of PAX-2 expression is a reliable marker of endometrial hyperplastic lesions rather than the loss of PAX-2 expression.