The contact effect on the performances of organic thin film transistors is studied here.A C 60 ultrathin layer is inserted between Al source-drain electrode and pentacene to reduce the contact resistance.By a 3 nm C 60 modification,the injection barrier is lowered and the contact resistance is reduced.Thus,the field-effect mobility increases from 0.12 to 0.52 cm 2 /(V·s).It means that inserting a C 60 ultra thin layer is a good method to improve the organic thin film transistor (OTFT) performance.The output curve is simulated by using a charge drift model.Considering the contact effect,the field effect mobility is improved to 1.15 cm 2 /(V·s).It indicates that further reducing the contact resistance of OTFTs should be carried out. The contact effect on the performances of organic thin film transistors is studied here. AC 60 ultrathin layer is inserted between Al source-drain electrode and pentacene to reduce the contact resistance. By a 3 nm C 60 modification, the injection barrier is lowered and the contact resistance is reduced. Thus, the field-effect mobility increases from 0.12 to 0.52 cm 2 /(V.s).It means that a C 60 ultra thin layer is a good method to improve the organic thin film transistor (OTFT) the output curve is simulated by using a charge drift model. With the contact effect, the field effect mobility is improved to 1.15 cm 2 /(V.s).It indicates that further reducing the contact resistance of OTFTs should be carried out .