Direct inlet/MS was used to investigate the pyrolysis pathway and the pyrolyzates of tobacco polyphenols as precursor of catechol which has been known as one of the most potent co-carcinogen from cigarette smoke. Caffeic acid, catechol and quercetin, catechol were detected from the pyrolyzates of chlorogenic acid and rutin, respectively. Interrelationship between polyphenols from tobacco leaf and catechol from cigarette smoke was investigated by using HPLC and GC. These results reveal that chlorogenic acid is the most significant precursor of catechol in cigarette smoke.