In an organic solvent system, the preparation of biodiesel from waste oil and methanol was performed by transesterification under the catalysis of immobilized lipase, namely Novozym 435. Results : The optimum reaction conditions are absolute ether dose 0.8mL/goil, catalyst dose 10%, molar ratio of methanol/oil 3.5: 1, reaction temperature 40℃ and reaction time 12h. Under the optimum reaction conditions,the conversion of waste oil to methyl esters reaches 92.15%. It is revealed that a three - step methanolysis protocol can protect the immobil...