Organic thin film transistors(OTFTs) based on poly(3-hexylthiophene)(P3HT)/Zinc oxide(ZnO) nanorods composite films as the active layers were prepared by spray-coating process. The OTFTs with P3HT/ZnO-nanorods composite films owned higher carriers mobility than the OTFT based on pure P3 HT. It can be found that the mobility of OTFTs increased by 135% due to ZnO-nanorods doping. This was attributed to the improvement of the P3 HT crystallinity and the optimization of polymer chains orientation. Meanwhile, because of the distinction of work function between P3 HT and ZnO, the majority carriers would accumulate on either side of the P3HT-ZnO interface which benefited carrier transfer. The influence on the mobility of composite film was studied. In addition, the threshold voltage of devices changed positively with the increase of ZnO-nanorods due to the decrease of electrostatic potential for P3HT/ZnO-nanorods composite films. The effect could be explained by the energy level theory of semiconductor. Organic thin film transistors (OTFTs) based on poly (3-hexylthiophene) (P3HT) / Zinc oxide (ZnO) nanorods composite films as the active layers were prepared by spray-coating process. The OTFTs with P3HT / ZnO-nanorods composite films owned Higher carriers mobility than the OTFT based on pure P3 HT. It could be found that the mobility of OTFTs increased by 135% due to ZnO-nanodods doping. This was attributed to the improvement of the P3 HT crystallinity and the optimization of polymer chains orientation . Moreover, because of the distinction between work function between P3 HT and ZnO, the majority of carriers would accumulate on either side of the P3HT-ZnO interface which benefited carrier transfer. The influence on the mobility of composite film was studied. threshold voltage of devices changed positively with the increase of ZnO-nanorods due to the decrease of electrostatic potential for P3HT / ZnO-nanorods composite films. The effect could be explained by the energy level theory of sem iconductor.