In this investigation, Mahua Oil Ethyl Ester was prepared by transesterification using sulfuric acid (H2SO4) as catalyst and. tested in a 4-stroke direct injection natural aspirated diesel engine. Tests were carried out at constant speed of 150,0 rev/min at different brake mean effective pressures. Results showed that brake thermal efficiency of Mahua Oil Ethyl Ester (MOEE) was comparable with diesel and it was observed that 26.36% for diesel whereas 26.42% for MOEE. Emissions of carbon monoxide, hydrocarbons, oxides of nitrogen and Bosch smoke number were reduced around 58, 63, 12 and 70%, respectively, in case of MOEE compared to diesel. Based on this study, MOEE can be used a substitute for diesel in diesel engine. (c) 2004 Elsevier Ltd. All rights reserved.