Several automobile manufacturers are interested in investigating of dual fuel internal combustion engines, due to high efficiencand low emissions. Many alternative fuels have been used in dual fuel mode for IC engine, such as methane, hydrogen, and natural gas. In the present study, a reactivity controlled compression ignition (RCCI) engine using gasoline/diesel (G/D) dual fuel has been investigated. The effectof mixing gasoline with diesel fuel on combustion characteristic, engine performance and emissions has been studied. The gasoline was injected in the engine intake port, to produce a homogeneous mixture with air. The diesel fuel was injected directly to the combustion chamber during compression stroke to initiate the combustion process. A direct injection compression ignition engine has been built and simulated using ANSYS Forte professional code. The gasoline amount in the simulation varied from (50%-80%) by volume. The diesel fuel was injected to the cylinder in two stages. The model has been validated and calibrated for neat diesel fuel using available data from the literature. The results show that the heat release rate and the cylinder pressure increased when the amount of added gasoline is between 50%-60% volume of the total injected fuels, compared to the neat diesel fuel. Further addition of gasoline will have a contrary effect. In addition, the combustion duration is extended drastically when the gasoline ratio is higher than 60% which results in an incomplete combustion. The NO emission decreased drastically as the gasoline ratio increased. Moreover, addition of gasoline to the mixture increased the engine power, thermal efficienc and combustion efficienc compared to neat diesel fuel.