In this study, the effects of premixed ratio of gasoline on the combustion and exhaust emissions were investigated in a single-cylinder, HCCI-DI engine. The experiments were performed at the engine speed of 2200 rpm and maximum brake torque operating conditions. The amount of the premixed gasoline was controlled by a programmable electronic control unit (ECU) and the gasoline injection was conducted into the intake air charge using low pressure fuel injection system. The premixed ratio of gasoline was changed 10 %, 20 % and 30 % and results were compared to neat diesel operation. The experimental results show that two stage combustion (premixed HCCI combustion and diffusion combustion) was found. Increasing in-cylinder pressure and heat release was observed in the first stage of combustion. In the second stage of combustion, lower diffusion combustion was occurred with premixed gasoline fuels. Cycle-to-cycle variations were very small with the diesel fuel and 10 % gasoline premixed fuel. Audible knocking occurred with 30 % gasoline premixed fuel ratio. NO x-soot trade-off characteristics were changed and improvements were found simultaneously. NO x and soot emissions were decreased up to 16 % and 65 % respectively, while exhaust gas temperature decreased by 22 %. On the other hand, CO and HC emissions increased.