Abstract: objective :To investigate the correlation between methylation of the ASC gene promot-er region and the clinical characteristics of patients with non- small cell lung cancers and to determinewhether the methylation of the ASC gene can be reversed by a demethylation agent. Methods :Methyla-tion-specific PCR (MSP) was performed to detect methylation of the ASC gene promoter in 48 patientswith NSCLC and in 3 lung cancer cell lines, and RT-PCR was employed to examine the restoration ofexpression in lung cancer cell lines after treating with the demethylation agent 5-aza-2'-deoxycytidine. Results :The frequency of ASC gene methylation in cancer tissues was significantly different from thatin adjacent normal tissues (47.9% to 8.3%, P<0.001). There was a higher rate of ASC gene methylationin the tumor tissues of heavy smokers (P<0.05) and in early stage NSCLC(T1) (P<0.05). Expression ofthe methylated ASC gene was restored after cells were treated with the demethylation agent. Conclu-Sions :Methylation of the ASC gene promoter may be related to NSCLC caused by smoking and may bean early event in the genesis of NSCLC. Methylated ASC gene promoters may be a target in the treat-ment of NSCLC.