An experimental study has been carried out on the combustion characteristics of a newly proposed direct-injection stratified-charge SI engine. A water-cooled, 4-cylinder, 4-stroke-cycle diesel engine with a square piston cavity was modified to permit the installation of a spark plug. Charge stratification was accomplished with two-stage fuel injection. The main fuel was injected at the early stage of the induction stroke to form a lean homogeneous mixture, and the auxiliary fuel was injected just before the spark firing to produce a rich mixture near the spark plug. The results showed that the lean limit was extended up to approximately the air-fuel ratio of 25 without increasing in fuel consumption and HC emissions. The optimum quanTITY of auxiliary fuel was found to extend the lean limit and to reduce the fuel consumption. Charge stratification caused a reduction in the ignition delay.