Hydrogen can be produced by electrolyzation with renewable electricity and the combustion products of hydrogen mixture include no CO, CO2 and hydrocarbons. In this study, engine performance with hydrogen / diesel dual fuel (hydrogen DDF) operation in a multi-cylinder diesel engine is investigated due to clarify advantages and disadvantages of hydrogen DDF operation. Hydrogen DDF operation under several brake power conditions are evaluated by changing a rate of hydrogen to total input energy (H2 rate). As H2 rate is increased, an amount of diesel fuel is decreased to keep a given torque constant.When the hydrogen DDF engine is operated with EGR, Exhaust gas components including carbon are improved or suppressed to same level as conventional diesel combustion. In addition, brake thermal efficiency is improved to 40% by increase in H2 rate that advances combustion phasing under higher power condition. On the other hand, NOx emission is much higher than one of conventional diesel engine. Additionally, hydrogen DDF engine operation at higher engine load with high H2 rate is limited by a variability of in-cylinder pressure among each cylinder. Mixing hydrogen and intake air will be encouraged to introduce homogeneous mixture to each cylinder.Following the result of increase in NOx emission under hydrogen DDF operation, we evaluate the effects of EGR (Exhaust Gas Recirculation) on the performance. Under 40kW power and H2 rate 55% condition. When EGR rate is around 20 %, the emission level of hydrogen DDF engine is at the same level as a mass-production diesel engine for heavy duty vehicles. However, there're still problems on soot emission and cylinder-to-cylinder pressure variation.