Abstract: The generation of polycyclic aromatic hydrocarbons by pyrolysis of cholesterol, stigmasterol,β-sitosterol, ergosterol, campesterol and the thermogravimetric behavior of those sterols were investigated by pyrolysis instrument and thermogravimeter. Cholesterol, stigmasterol,β-sitosterol and ergosterol were added into cigarettes in order to validate the relationships between the sterol addition rate and the delivery of polycyclic aromatic hydrocarbons in mainstream smoke. The results showed that:1) Polycyclic aromatic hydrocarbons, especially those having less rings, were generated from the five sterols in the environment of high temperature and hypoxia. The pyrolytic products from the said sterols and their distribution rules were similar. Taking stigmasterol as an example, naphthalene and its derivatives accounted for 35.44% of total pyrolytic products of stigmasterol. 2) Only one phase of weight loss was observed and the pyrolysis basically completed in the range of 300-400℃. It was speculated that cracking reactions might be the dominant factor in the pyrolysis process of the five sterols. 3) The addition rates of sterols in cigarette and the delivery of benzoa pyrene in mainstream smoke showed an obvious positive correlation; the contribution of stigmasterol was particularly significant, by adding 2 times its content in cigarette, benzoapyrene delivery increased by 17.8%.