Abstract: Objective To detect the expressions of p16, Cyclin D1, COX-2 protein in various hyperplastic lesions of endometrium and explore the potentiality of these proteins as markers in diagnosis of EIN and endometrioid adenocarcinoma. Methods Expression of p16, Cyclin D1,COX-2 protein was detected in 131 cases of various hyperplastic endometrial lesions by immunohistochemistry and analyzed by statistics. Results (1) 26 EIN and 68 benign hyperplasia were rediagnosed in 94 endometrial hyperplasia. (2) There was no significant differences in positive expression and overexpression rate of p16 and Cyclin D1 among proliferative endometrium, benign hyperplasia, EIN and endometrioid adenocarcinoma ( P >0.05). (3) Positive expression and overexpression rate of COX-2 in EIN and endometrioid adenocarcinoma was significantly higher than those in proliferative endometrium and benign hyperplasia( P <0.01)，but difference was not obvious in EINand endometrioidadenocarcinoma（ P >0.05）. Conclusion In contrast to expression of p16 and Cyclin D1, overexpression of COX-2 may be an early event in the tumorigenesis for endomerioid adenocarcinoma;andthis protein was useful tumor markers in distinguishing benign hyperplasia from EIN and endometrioid adenocarcinoma.