The efficiency of the processing of diesel fuel for improving its environmental properties was assessed. The composition of polycyclic aromatic hydrocarbons (PAH) in the fuel before and after its treatment as well as in exhaust gases was studied. The amount of carcinogenic PAH was found to be 2-3 times smaller after the treatment. The concentration of carcinogenic N-nitrosoamines in fuel and treated products was determined. A change in the concentration of PAH during storage was revealed. The dynamics of variation in the amount of PAH during storage was described; it was found that the treated fuel had a more homogeneous structure and smaller propensity to sediment formation than the initial fuel.