The present paper describes the results of an experimental activity performed on a small diesel engine for quadricycles, a category of vehicles that is spreading in Europe and is recently spreading over Indian countries. The engine is a prototype three-cylinder with 1000 cc of displacement and it is equipped with a direct common-rail injection system that reaches a maximum pressure of 1400 bar. The engine was designed to comply with Euro 4 emission standard that is a future regulation for quadricycles. It is worth underlining that the engine can meet emission limits just with EGR system and a DOC, without DPF. Various diesel/RME blends were tested; pure diesel and biodiesel fuels were also used. The investigation was carried out at the engine speeds of 1400, 2000 and 3400 rpm and full load. Combustion characteristics of both blended and pure RME were analyzed by means of in-cylinder pressure and heat released histories. A smoke meter was used to determine the particulate matter concentration. The sizing and the counting of the particles were performed in the range 5.6-560 nm. Gaseous emissions were measured at the exhaust. Lower exhaust emissions were measured when the engine runs with pure RME with respect to diesel fuel in terms of CO, HC, NOx, PM and particle number. From the analysis of the data it can be argued that a proper engine calibration could further optimize the combustion process and emission formation when the engine is fueled with RME blends.