The porcine pancreas lipase(PPLipase) was modified by Tweens in the ethanol-water solution in this paper,the efficiency of the modification of the PPLipase was determined by incorporation of interesterification of oils catalyzed by them,and the thermal stability of the modified PPLipases and the original PPLipase was also studied.The results indicate that the modification could be finished in 30min at 40℃,however the optimum conditions for different Tweens were not the same.For Tween20,the optimum conditions were the ratio of ethanol to water 1∶2(v/v),the amount of Span20 5%.For Tween40 and Tween65,the optimum conditions were the ratio of ethanol to water 1∶2(v/v),the amount of them 1520%.For Tween65,the optimum conditions were the ratio of ethanol to water 1∶2(v/v),the amount of Tween 20%.For Tween80,the optimum conditions were the ratio of ethanol to water 1∶3(v/v),the amount of Tween80 5%.For Tween85,the optimum conditions were the ratio of ethanol to water 1∶3(v/v),the amount of Tween85 15%.The catalytic activity of the modified PPLipase was higher than that of the original PPLipase in the range of 40℃ to 80℃ and the modified lipases showed the better catalytic activity in the range of 40~70℃.The modification of PPLipase by Tweens could improve the catalytic activity and thermal stability dramatically.