Rubber seed oil and methyl ester of rubber seed oil have been evaluated as fuel for diesel engines. Engine performance tests, spray characteristics measurements and fuel property evaluations were performed using the above materials. The study indicated that rubber seed oil has fuel properties very similar to other vegetable oils. Compared with diesel oil, rubber seed oil meets the ASTM limits for cetan number, flash point, and total and active sulphur, water and sediment contents. But it failed to meet the ASTM limits for viscosity, ash content, carbon residue, cloud and pour points. Higher viscosity was found to affect the characteristics of the fuel spray. Fuel properties of methyl ester of rubber seed oil were more close to those of diesel oil. Engine performance tests indicated that rubber seed oil, methyl ester of rubber seed oil and blends of these with diesel oil were very much similar to diesel oil in terms of power productivity, thermal efficiency and specific fuel consumption.