Diesohol fuel is a mixture of diesel and bioethanol fuels in which the ratio of bioethanol is less than 15%. In this research work, performance of a tractor engine (Massey Ferguson 399) using diesohql fuel was investigated. In these circumstances, the concentration of UHC and CO2 emissions in the exhaust pipe were measured and analyzed. The engine was run at several speeds (1600-2000 rpm). The obtained results reveal that, when using diesohol fuels, the power and torque of the MF-399 tractor engine are increased by 3.17-8.50% and 1.75-10.28% respectively when compared to diesel fuel. This is due to a relatively more complete combustion of ethanol because of its high oxygen content. The fuel consumption and specific fuel consumption are also increased by 7.32-15.81% and 4.37-7.44% respectively due to low calorific value of ethanol compared to diesel fuel. The analysis showed that when diesohol is used, the rate of UHC is decreased but CO2 emission is increased. In brief, by using diesohol fuels, especially E6 blend in comparison to diesel fuel, engine performance and emissions are improved without any changes in engine structure for diesohol application. (C) 2013 Elsevier Ltd. All rights reserved.