Abstract: Objective To explore the expression of apoptosis-relate d factors Bax in the lung cancer and the relationship of the expression of Bax t o apoptosis and/or proliferation. Methods TUNEL technique was a p plied to detect the apoptosis and the immunohistochemistry was applied to d etect Bax oncoprotein and PCNA.The apoptotic index (AI) and mitotic index (MI) were de fined. Results The amount of Bax oncoprotein of lung cancer tiss u es increased obviously,P＜0.01.The Al and Ml of lung cancer were higher t ha n those of the lung benign cases,P＜0.01;The Al of cancer cases with Bax-po sitive was obviously higher than that with Bax-negative, P＜0.01. Conclusion The amount of Bax oncoprotein increased obviously an d the apoptosis and proliferation were active in the lung cancer.Bax played an important role in the apoptosis in the lung cancer.