Oil seed plants have been one of the biomass sources of fuel. Vegetable oils may be employed in CI engines as an alternative fuel. In this study, diesel fuel properties of sunflower oil were determined and long term engine tests of sunflower oil were performed. Engine tests were conducted at a speed of 1600 rpm under part load condition for 50 h with a single-cylinder (volume: 1007 cm(3)) direct injection, air cooled diesel engine, having a bore/stroke ratio of 108:110 mm. An overall evaluation of results indicates that the sunflower oil can be proposed as a possible candidate for diesel fuel.