In this work researches of the used methyl ester of vegetable oil and their mixes with diesel fuel in various proportions as fuel for the purpose of studying of performance data of the engine and content of emissions were carried out. Biodiesel fuel was produced by transesterification in the presence of the catalyst of sodium hydroxide (NaOH) and potassium hydroxide (KOH) in proportions of 20% and 100% (on volume) which usually are called B20N, B100N, B20K, B100K, respectively. The experiment was performed in the load range of 0%, 25%, 50%, 75% and 100%. It has been established that, compared with diesel fuel, when testing obtained biodiesel, CO emissions are reduced by 13.63%, 32.2% for mixtures of B20N and B100N at full load and by 4.5%, 32% for B20K and B100K, respectively. Compared to diesel fuel, biodiesel fuel and its mixtures showed a significant reduction in emissions of CO, hydrocarbons, smoke and particulate matter. However, the content of nitrogen oxides in used vegetable oil biodiesel was slightly higher than that of diesel fuel. The authors of the work conclude that the diesel engine can operate satisfactorily on biodiesel fuel and its mixtures with diesel fuel without any engine modifications.