Abstract: Diesel oil (0#) was used as the reaction solvent for lipasecatalyzed esterification of high acid value waste oil to produce biodiesel; in this way, the resultant mixture could be directly used as diesel oil and the troublesome operation of distillation and reclamation of solvent was avoided. The optimum conditions for esterification of high acid value waste oil were as follow: the amount of Novozyme435 being 10% based on oil weight, initial molar ratio of methanol to oil being 2∶1, weight ratio of diesel oil to waste oil being 5∶1, shaking rate of 170r/min; the esterification conversion of fatty acid to methyl ester reached 95.10% after reaction at 50℃ for 2h and the stability of Novozyme435 was also improved obviously with diesel oil as solvent. Moreover, the diesel oil may dilute the rudimental phospholipids harmful to lipase in the waste oil slightly, though the degumming treatment of waste oil is still a key factor to determine the stability of Novozyme 435 and the feasibility of producing biodiesel from high acid value waste oil.