The influences of fuel vaporization on the stratified mixture preparation of a direct injection gasoline engine were investigated by means of altering fuel property. Iso pentane was selected for the evaluation. The mixture preparation in the both case of gasoline and iso pentane were numerically simulated with 3-D CFD. The experimental examinations, such as engine performance tests, the incylinder visualization and the cylinder pressure analysis, were also given. It was confirmed that the iso-pentane vaporized much quicker than gasoline, whereas there were not many differences in the fuel distribution at the ignition timing. Therefore, the effect of the injection timing on the indicated mean effective pressure, exhaust NOx and HC emissions and the heat release rate was almost same between the two fuels.