Objective: To investigate the expression and clinical significance of Fas and FasL in lung cancer. Methods: SP immunohistochemical technique was used to detect the expression of Fas and FasL in 46 cases of lung cancer and 30 cases of adjacent non-neoplastic tissue. Results: Down-regulation of Fas and up-regulation of FasL were found in lung carcinoma. The levels of Fas expression in squamous cell carcinoma, adenocarcinoma and SCLC were significantly lower than that of adjacent normal tissues ( P＜ 0. 01), while the expression levels of FasL were the opposite (P＜0. 05). Fas expression was associated with high histological grade and no metastasis (P＜ 0.05).FasL expression was related to histological grade, late clinical stage and metastasis ( P＜ 0.05). Both Fas and FasL expression was not related to the histological type of lung cancer ( P＞ 0.05). The level of Fas expression was negatively related to that of FasL ( P ＜ 0.05). Conclusion :Down-regulation of Fas and up-regulation of FasL may work in coordination with the occurrence, development and metastasis of lung cancer. Fas or FasL can be used as one of markers in early diagnosis of lung cancer.Therefore, the combined assay may be helpful in predicting the grade of malignancy and the prognosis of patients with lung cancer.