In the present study, the effects of the neat biodiesel ( rapeseed methyl ester, RME) fueled diesel engine with the use of EGR on the particle size distribution were examined. The combustion of REM significantly improves the engine smoke and total particle mass but increases both NOx and particle concentration with low aerodynamic diameters (< 0.091 mu m) when compared to the diesel (ultralow sulfur diesel, ULSD) fueled engine. Although the particle size and mass distribution were not affected significantly by the different EGR additions, the particle total number and mass were increased considerably for both fuels. For the RME fueled engine, the EGR addition reduces the particles in the lowest aerodynamic diameter measured ( 0.046 mu m). The use of EGR better suits the RME combustion, as apart from resulting in the higher NOx reduction, it maintained the smoke ( soot, particulate matter) at relatively low levels. The results are also confirming that it is challenging to reduce simultaneously total particle mass without increasing the number of particles at low aerodynamic diameters. Furthermore, the lower RME calorific value compared to ULSD results in increased fuel consumption, although the engine efficiency was not noticeably affected.