The effects of premixed fuels(diesel or n-heptane) and exhaust gas recirculation on combustion and exhaust emission characteristics in a DI diesel engine were experimentally investigated. To improve homogeneity of fuel-air mixture in the conventional diesel engine, the premixed fuel is injected by high pressure(5.5 MPa) into the premixing chamber prior to engine cylinder, And several additional systems such as an EGR system, air heating system and back pressure control system were equipped in the DI diesel engine. The results showed that premixed fuel-air mixture undergoes typical HCCI combustion prior to the combustion of DI diesel fuel. The ignition timing of HCCI combustion is delayed by application of EGR, and it also shows that HCCI combustion can be controlled by an EGR.