In recent years, much interest has been devoted to bio-fuels because of their beneficial effects on environment, agriculture and economic development. Raw vegetable oil – a kind of bio-fuels, still exits many downsides, is potential renewable fuel replaced for ever-exhausted fossil fuel. In this report, vegetable oil which is available in the South of Vietnam such as raw coconut oil is studied by heating up different temperature with the aim at decreasing its high viscosity and density and meeting the fuel requirements. The experiments are conducted on heated coconut oil (HCO) and fossil diesel oil (DO) using an 80hp of small marine diesel engine. The results of engine performance as using DO and HCO included engine power (Ne), specific fuel consumption (SFC), thermal efficiency (TE), emission characteristics such as carbon monoxide (CO), unburned hydrocarbon (HC), smoke, nitrogen oxides (NOx) at internal feature are measured. The experiment results show higher SFC, CO, HC and smoke emissions, and lower TE, and NOx emissions for HCO with respect to DO. In addition, this study also reveals that, 1000C of HCO is said to be the most suitable heating temperature as getting the engine performance equals to DO.