Abstract: ObjectiveTo detect the promoter hypermethylation status of runt-related transcription factor 3 (RUNX3) gene in serum DNA of non-small cell lung cancer patients and to discuss its clinical significance. MethodsSerum DNA was extracted from 62 patients with NSCLC 30 patients with benign pulmonary disease, and 16 health subjects with medical check-up.The methylation status of RUNX3 gene was detected by MSP and the correlation of methylation profiles with clinical characteristic was statistically analyzed. ResultsAberrant promoter methylation of RUNX3 was found in 25 of 62 (40.32%) NSCLC patients,but in none of patients with benign pulmonary disease and health subjects with medical check-up（Fisher exact probabilities test,P<0.05）. The promoter hypermethylation of RUNX3 correlated with histopathology （χ2=4.12，P<0.05）and clinical stages（Fisher exact probabilities test,P<0.05），but not with age,gender,smoking index or differentiation in NSCLC patients. ConclusionThe promoter hypermethylation of RUNX3 may play an important role in the tumorigenesis and progression. It is hopeful to become a promising novel biomarker for diagnosis in NSCLC.