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Biodiesels are promoted as alternatives to fossil fuels and their applications in diesel engine have been studied extensively. However, the size distribution of polycyclic aromatic hydrocarbons (PAHs) and generator particulate material (GPM) emitted from heavy-duty diesel generator fueled with biodiesel blends has seldom been addressed. Seven different biodiesel blends with Volume fractions of biodiesel ranging from 0% to 30% were studied. Experimental results indicate that the mean reductions of sum of PAHi/GPM(0.056-18) (generator particulate material with aerodynamic diameter 0.056-18 mu m) and BaP(eq)i [=(benzo[a]pyrene equivalent)i]/GPM(0.056-18) of B5, B10, B15, B20, B25 and B30 are (-8.21%, -5.72%), (-36.7%, -29.7%), (-1.25%, 2.32%), (16.2%, 18.6%). (33.4%. 35.0%) and (40.5%, 42.4), respectively, compared with BO. Both PAHi/GPMi and BaP(eq)i/GPMi in stage 1 (0.056 - 0.166 mu m) and stage 2 (0.166 - 0.31 mu m) of all test fuels are higher than those in the other stages due to higher specific Surface area of smaller particles. It is also observed that there are more highly toxic PAHs in stage 2. It Should be noticed that the trend of particle-phase PAH contents is different from the trend of particle-phase PAH concentration and opposite to the trend of total GPM(0.056-18) emission. The differences are due to a higher number of particles with diameters between 0.056 arid 0.31 mu m. The above results indicate that fuel blends with less than 15% biodiesel would increase PAH content at particle size between 0.056 and 0.31 mu m. Therefore, the blending fraction should be between 15% and 30%. Moreover, particle-size control is needed in future emission regulations which would necessitate further improvements in combustion quality. Besides, researches on health effects of biodiesel blends are needed as well. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.