Abstract: In order to improve the lipase activity of the Rhizopus oryzae strain which is used for producing biodiesel fuel, ultraviolet mutation is employed in this research. The hydrolytic lipase activity and synthetic lipase activity of the selected strain R. oryzae LY6 was 433% and 112% as much as that of the original strain, reaching to 4.33 and 0.28 U/mL respectively. The maximum hydrolytic lipase activity of R. oryzae LY6 was at pH value 7.0. The immobilized R. oryzae LY6 as whole cell catalyst was used to catalyze transesterification of soybean oil. When the ratio of methanol to soybean oil is 3:1, the content of methyl ester in biodiesel fuel was 87.3%, which is 41.0% higher than the original one. When the ratio of methanol to soybean oil is 4:1, the content of methyl ester was 96.1%, which is 16.8% higher than the original one.

Key words: Rhizopus oryzae, ultraviolet mutation, lipase, biodiesel fuel