Objective To evaluate the clinical significance of carcinoembryonic antigen (CEA),cancer antigen 125 (CA125),carbohydrate antigen 19-9 (CA19-9) and eytokeratin 21-1 fragment (CYFRA21-1) assays of sputum in patients with lung cancer. Method Fifty-two cases with lung cancer and 46 cases with benign lung diseases underwent detection of CEA ,CA125 ,CA19-9 and CYFRA21-1 in sputum by using the method of chemi-luminescent enzyme immunoassay. Results The levels of CEA,CA125,CA19-9 and CYFRA21-1 in sputum of 52 cases with lung cancer were (27.6±31.2) μg/L, (76.4±65.2)kU/L, (56.1±31.6) kU/L and ( 25.2±9.1 )μg/L respectively. But the levels of those of 46 cases with benign lung diseases were (6.1±7.5)μg/L, (23.7±7.9) kU/L, (17.3±10.2) kU/L and (1.2±1.7)μg/Lrespectively. The levels of these tumor markers in sputum in patients with lung cancer were significantly higher than those in patients with benign lung diseases(P< 0.01 ). The diagnostic sensitivity of CEA,CA125,CA 19-9 and CYFRA21-1 in sputum in 52 cases with lung cancer was 42.3%( 22/52 ), 46.2% (24/52), 36.5%( 19/52 ) and 51.9% (27/52) respectively ( P > 0.05 ). Among the cancer patients, the sensitivity of sputum CEA in patients with adenocareinoma was significantly higher than that in patients with squamons cell carcinoma (X2= 4.193, P < 0.05 ) ; while the sensitivity of sputum CYFRA21-1 in patients with squamous cell carcinoma was significantly higher than that in patients with adenocarcinoma ( X2 = 4.806,P < 0.05 ). The sensitivity of CA125 in advanced lung cancer( Ⅲ +Ⅳ stage) was higher than that in early lung cancer( Ⅰ+Ⅱstage) (X2= 5.202,P < 0.05 ). Compared with the single tumor marker assaying, the combination of CEA,CA 125, CA 19-9 and CYFRA21-1 in sputum could significantly improve the sensitivity and accurate value in the diagnosis of lung cancer (P<0.05). Conclusion To assay CEA,CA125,CA1g-9 and CYFRA21-1 in sputum is valuable in diagnosis of lung cancer, and the combination of CEA,CA125,CA19-9 and CYFRA21-1 in sputum can significantly improve sensitivity and accurate value in the diagnosis of lung cancer.