Abstract： Objective To investigate the expression and correlation of phosphatase and tensin homologue deleted on chromosome ten(PTEN)， epidermal growth factor receptor(EGFR) and Ki-67 in human thymic tumors, and their possible role in tumor genesis， infiltration and metastasis. Methods The expression of PTEN， EGFR and Ki-67 were detected by using SP immunohistochemical technique in 45 cases of thymic tumors and 5 cases of normal thymic tissues. Results In 5 cases of normal thymic tissues, the expression of PTEN was bly positive, whereas EGFR and Ki -67 were weakly positive or negative. In 45 cases of thymic tumors, the positive ratio of PTEN were significantly reduced from benign thymoma， invasive thymoma to thymic carcinoma (χ2=7.808, P=0.020), but the positive ratio of EGFR and Ki-67 were gradually increased(χ2=8.032, 0.018，7.006；P=0.030). The positive ratio of PTEN， EGFR and Ki-67 protein were significantly related to Levine classification, Masaoka staging and lymph node metastasis (Plt;0.05). PTEN positive cases were negatively correlated with EGFR and Ki-67(r=－0.632，－0.653；Plt;0.01), EGFR positive cases were positively correlated with Ki-67 in thymic tumors(r=0.807,Plt;0.01). Conclusions Reduced or absent PTEN and increased EGFR and Ki-67 expression might play an important role in the genesis， invasiveness and metastasis of thymic tumors. The expression of PTEN is bly associated with the expression of abnormal EGFR and Ki-67. Detection of the three protein expressions simultaneously might be more helpful in making an early diagnosis of the tumors jndgement of theirs malignant degree，invasiveness and metastasis capacity, as well as the prognosis.