A method for producing vegetable oil fuel with low viscosity, including a transesterification step P.sub.1 with respect to vegetable oil with triglyceride structure having unsaturated fatty acid, an ozone treatment step P.sub.2 with respect to unsaturated fatty acid methyl ester generated in the transesterification step P.sub.1, and a reduction step P.sub.3 with respect to the ozonide generated in the ozone treatment step P.sub.2.