Objective To investigate the clinical value of serum tumor marker isocitrate dehydrogenase 1(IDH1)in the diagnosis of lung cancer. Methods The general data were collected in lung cancer patients and non-lung cancer patients.The serum level of IDH1 was detected by enzyme-linked immunosorbent assay to evaluate its clinical significance in diagnosing lung cancer. Results The serum IDH1 level was significantly higher in lung cancer patients than in non-lung cancer patients [(7.12±6.98)ng/ml vs.(2.09±1.83)ng/ml,t=11.540,P<0.001].The serum IDH1 level in patients with adenocarcinoma or squamous cell carcinoma was significantly higher than that in patients with small cell lung cancer [(7.91±7.26)ng/ml vs.(2.76±2.27)ng/ml, t=6.345,P<0.001].The sensitivity of IDH1 in detecting lung cancer,stage Ⅰ/Ⅱ lung cancer,and stage Ⅲ/Ⅳ lung cancer was 47.4%,49.1%,and 46.3%,respectively. Conclusions Serum IDH1 has high sensitivities and specificities in the diagnosis and differential diagnosis of non-small cell lung cancer(squamous cell carcinoma and adenocarcinoma)and small cell lung cancer as well as the auxiliary diagnosis of stage Ⅰ and Ⅱ lung cancer.It is a valuable marker for the auxiliary diagnosis of lung cancer.