The main objectives of this study are the assessment of fine particles (PM2.5) and carbonyl compound emissions from an electrical generator fueled with biodiesels and the evaluation of the efficiency of a commercial 4-way catalytic converter toward these pollutants. Two different biodiesels were used: Soybean Oil fatty acid Methyl Esters (SOME) and Waste Cooking Oil fatty acid Ethyl Esters (WCOEE). Several biodiesel blends with petroleum diesel were tested (0%vol, 7%vol, 20%vol, and 50%vol). For all blends it was shown that particles are mainly composed of ultrafine particles with a diameter below 0.4 mu m. The presence of a 4-way catalyst allows the reduction of the total number of particles emitted by at least 97%. However, the fraction of the smaller particles (PM0.1), which are particularly harmful to health, becomes predominant. The origin and concentration of biodiesel introduced in the fuel influence both the total number of emitted particles and their size distribution. The different behavior of the two biodiesels used in this study regarding particulate matter emissions is linked to the fuel properties. Interesting results are obtained from the measurement of carbonyl compounds emissions. This study reveals that the presence of biodiesel in the fuel has a major effect on acrolein, propanal, and acetone production. Moreover, it appears that the 4-way catalyst is not efficient toward carbonyl compound conversion.