Increasing cost and scarcity of petroleum resources have promoted research in alternative fuels for internal combustion engines. Among various possible options, fuels derived from triglycerides (vegetable oils/animal fats) are promising substitutes of fossil diesel fuels. Vegetable oil poses some problems when subjected to prolonged use in compression ignition engines because of its high viscosity as reported by researchers. In this present research, experiments were designed to study the effect of low viscous rice bran oil on engine's combustion. The viscosity of the oil was reduced by increasing the fuel temperature. A single cylinder, 5 hp, four stroke, constant speed, water cooled, direct injection diesel engine typically used in stationary operation was used for the experiments. The acquired data were analyzed for various parameters, such as thermal efficiency, brake specific fuel consumption, exhaust emission of CO, CO2, HC, and NOx gases. While operating the engine on rice bran oil (preheated and blends), performance was found to be very close to that of mineral diesel for lower blend concentrations. The preheated oil's performance was slightly inferior in efficiency due to low heating value. As for the pollution point of view, it can perform well for the unmodified engine for a long period operation without any ignition problems. People of rural areas can use this for their agricultural engines without modification.