In this study, burning oil of biomass (BOB) was derived from biomass corncob tar by distillation. The fuel BOB1 was extracted from biomass corncob tar by distilling temperature range from 110 to 220 degrees C, the fuel BOB2 was extracted from biomass corn tar by distilling temperature over 220 degrees C. This paper presents that the results in the physical characteristic of BOB as an alternative fuel and a comparative control experiences in unmodified diesel engine. Engine power performance, fuel consumption and emissions (CO2, CO, HC and NO) have been studied. There was no significant difference in performance between diesel fuel and mixed fuel. The mixed fuel operation produced low fuel consumption at the various loading. Mixed fuel 1 (mixed 10% BOB1 with diesel by volume) and mixed fuel 2 (mixed 10% BOB2 with diesel by volume) with 11.7 and 6.6% oil-economizing rate, had better oil-economizing compare to diesel fuel respectively. The mixed fuel 1 and mixed fuel 2 showed significant improvement at CO2 emissions. (c) 2005 Elsevier Ltd. All rights reserved.