Performance optimization of small diesel engines is greatly owing to the matched improvements between combustion chamber and fuel injection system. Fuel injection characteristics are especially important to realize optimum engine performance in all speed range.In recent years, lower noise and white smoke reduction during cold temperature operation have been strongly required for agricultural and industrial application, which are the same technical trend as automotive's. As these two requirements are in the trade - off relationship from a combustive point of view, it is very complicated to realize both at the same time. Therefore, fuel injection characteristics are analyzed in detail for important factors such as injection pressure pattern, its behavior and injection timing so that the aimed optimum engine performance is obtained.This paper describes an optimization example of achieving simultaneous reduction of white smoke and noise by fuel injection characteristics' improvements. Objective engine used for this study is 0.3ℓ/cyl with swirl chamber for agricultural and industrial use.