Soot and hydrocarbons are usually found in diesel exhaust gases. They are formed when the fuel is burnt out incompletely. Polycyclic aromatic hydrocarbons (PAH) are sorbed on the soot, and may cause cancerous diseases, asthma and other diseases. The purpose of this work was to evaluate the dependence of smoke opacity and amount of polycyclic aromatic hydrocarbons in engine emissions on multi-component biodiesel fuel composition. We analyzed the composition of exhaust gases when diesel engine was fuelled with rapeseed oil methyl esters (RME ), RME mixtures with linseed oil methyl esters (LSME ) and fatty acid methyl esters (FA ME) of animal origin, assessing the smoke opacity and qualitative and quantitative composition of PAH. It was determined that smoke opacity of exhaust gases decreases at different rotation speeds (1200 and 2000 min^-1) when the amount of FA ME, containing a greater amount of saturated fatty acids, is increasing.Total PAH concentration in exhaust gases of biofuel mixtures with pork lard fatty acid methyl esters (LME ) is lower than in the case of mixtures with beef tallow fatty acid methyl esters (TME ). The amount of PAH at a rotation speed of 1200 min^-1 reduced down to 57%, if compared to pure RME , and down to 30%, when the rotation speed was 2000 min^-1. In the exhaust gases of biofuel mixtures with pork lard fatty acid methyl esters there are fewer PAHs with highly expressed mutagenic and carcinogenic effects if compared to pure RME and its mixtures, containing tallow fatty acid methyl esters. The most effective from an environmental point of view is use of a fuel mixture containing 80% RME , 4% LSME and 16% LME.