The paper describes some advantages of using vegetable oils as a biofuel in diesel engines. It presents the results of an experimental study on a diesel engine of the D-245.12S model used in a light cargo truck ZIL 5301 "Bychok", which runs on the blend of sunflower oil methyl ester and diesel fuel. The authors prove that it is possible to improve significantly the emission index of combustion exhaust gases emitted from the analyzed engine diesel.