Mode transition between low temperature combustion and conventional combustion was investigated in a direct injection diesel engine. Low temperature diesel combustion was realized by means of high exhaust gas recirculation rate (69~73%) and early injection timing (-28~ -16 crank angle degree after top dead center) compared with those (20% exhaust gas recirculation rate and -8 crank angle degree after top dead center) of conventional combustion. Tests were carried out at different engine speeds and injection pressures.Exhaust gas recirculation rate was changed transiently by controlling each throttle angle for fresh air and exhaust gas recirculation to implement mode transition. Various durations for throttle transition were applied to investigate the effect of speed change of exhaust gas recirculation rate on the characteristics of mode transition. Indicated mean effective pressure, intake pressure, maximum pressure rise rate and real-time unburned hydrocarbon emissions in the exhaust manifold were analyzed transiently.At the early stage (10 - 20 cycles) of mode transition from low temperature diesel combustion to conventional combustion, combustion performance became unstable with high fluctuation in indicated mean effective pressure and rapid increase in maximum pressure rise rate. In the case of mode transition from conventional combustion to low temperature diesel combustion, combustion performance kept stable without substantial change in indicated mean effective pressure and maximum pressure rise rate. indicated mean effective pressure kept constant at the early stage, but decreased gradually to a lower level.Transient injection strategy, which modulated including injection timing and injection quantity, cycle to cycle was applied to reduce fluctuation of indicated mean effective pressure during mode transition. This process had the result that the range of fluctuation in indicated mean effective pressure decreased and maximum pressure rise rate was considerably reduced.