Abstract: Objective : To investigate the expression of P21, P27, bcl-2 and bax protein and their clinical significance in lung cancer. Methods The expression of P21, P27, bcl-2 and bax was detected respectively in 85 patients with lung cancer and 21 with benign pulmonary lesion by the immunohistochemical staining. Results : Positive rate of P21, P27, bcl-2, bax protein expression was 72.94%, 37.65%, 61.18% and 41.18%, respectively. There was a statistically significant difference in positive rates of these protein (P0.05). There was a close correlation between expression of bcl-2 and the histopathological types of lung cancer; the rate of bcl-2 in small cell carcinoma was the highest and that in adeocarcinoma was the lowest. The positive rate of P27, bcl-2 and the bax protein in higher differentiation group was significantly lower than that in lower differentiation group (P0.05). The positive rate of P21 and bcl-2 protein was correlated with the P-TNM stages (P0.05). Only expression of bax protein has relation with the lymph node metastasis. There was a correlation between P27, bcl-2 and the bax protein. Conclusion : The results suggest that P21, P27, bcl-2 and bax protein have relations with the genesis and development of lung cancer. The detection for these proteins will play an important part in clinical diagnosis and prognosis.