Abstract：Objective To study the clinical value of serum macrophages inhibitory cytokine-1 (MIC-1) level in patients with lung cancers. Methods The double antibody sandwich ELISA was used to detect serum MIC-1 level in 256 lung cancer patients, 44 benign pulmonary disease patients and 229 healthy persons. ELCIA and CLIA were used to detect the serum CEA, CA125, NSE, CYFRA21-1 and SCC level. Results MIC-1 concentration in lung cancer group was significantly higher than that in normal control group (P<0.001）and benign disease group (P<0.001). According to ROC curve and MIC-1 level of normal control group, the cut-off value of MIC-1 was set at 1000pg/mL, the specificity and sensitivity were 96.5% and 69.5% respectively. In different subtypes of lung cancer, the sensitivity of serum MIC-1 was highest in SCLC group than squamous-cell carcinoma and adenocarcinoma groups. The serum level of MIC-1 was higher in low differentiation group than high differentiation and differentiated groups（P<0.05）. The sensitivity of MIC-1 for early stage lung cancer was higher than CEA, CA125, NSE, SCC and CYFRA21-1 respectively .The sensitivity of MIC-1 for early stage lung cancer (stage I and stage II) was higher than the combination of the above five markers（stage I： 66.7% vs 50.0%；stage II：72.7% vs 69.0%）. The sensitivity of MIC-1 for stage I and stage II was improved to 77.1% 85.5% respectively in the combination of the six markers. Conclusion The present study is to confirm excellent clinical value of MIC-1 in a large sample of lung cancer. MIC-1 may be a new serum marker for lung cancer diagnosis.