The charge transport properties in a mixture of regio-regular (poly 3-hexylthiophene) (RR-P3HT) and Zinc Oxide nano particle (ZnO) have been studied using the photoinduced charge extraction by linearly increasing voltage (PhotoCELIV) technique. We have studied the effect of ZnO nanoparticle size (12 nm and 50 nm) on the charge transport properties by fixing the composition ratio of P3HT/ZnO hybrid. The PhotoCELIV mobility in P3HT/50nm-ZnO at room temperature is found to be 7.8×10-5cm2/Vs at an applied electric field of 2.5 ×104 V/cm, which increases to 1.7×10-4cm2/Vs for P3HT/12nm-ZnO composite. The temperature and electric field dependence of charge mobility in these composites have been studied and analysed using Gaussian disorder formalism. The obtained results suggest that the charge transport properties in P3HT/ZnO composite, at low ZnO concentrations, can be tuned by varying the size of the nanoparticle.