In this work, the methanol is added to the diesel fuel in the volumetric proportions of 5%-%10-%15 to diminish negative environmental impacts of diesel engines. The diesel-methanol blends in the various proportions are tested in a single-cylinder direct-injection diesel engine. According to the test results, the addition of methanol to the diesel fuel causes a maximum decrease of 13.07 % in the engine torque, and a maximum decrease of 12.54 % in the specific fuel consumption. On the other hand, the exhaust emission results show that the values of CO and CO2 decrease 38.4 % and 5.04%. However, the increase of 3.66% in the exhaust gas temperature causes the increase of 17.1% in the NOx emission. Also, a significant decrease of 39.37% in the smoke opacity is observed compared to that of the diesel fuel. Although the addition of methanol to diesel fuel causes a slightly decrease in the engine performance, the diesel-methanol blends have a reasonable and considerable positive effect on environmental concerns of diesel engines.