This paper compares the characteristics of combustion of CNG by the pilot homogeneous charge compression ignition of gasoline and combustion of stratified, overall lean SI combustion of CNG. Homogeneous charge of gasoline is created by injecting the fuel in the manifold and the charge is heated by an air heater in order to achieve HCCI combustion of gasoline that ignites the direct-injected and stratified CNG at 80 BTDC. The combustion characteristics obtained are compared with that of CNG by spark ignition. The results show that there are significant effects on combustion characteristics, HC, CO and NO emissions. HCCI combustion has higher fuel conversion efficiency compared to SI and less emissions within certain range of loads.