ZnO/rGO composites are prepared by the conventional solid-state reaction method. Structural properties of prepared compounds were studied using XRD technique and it is observed that all the samples are crystallized in wurtzite structure. Electrical resistivity measurements were carried out using four probe method employing a closed cycle refrigerator. With addition of rGO, colossal reduction in the resistivity is observed which is about three orders of magnitude smaller than that of the pure sample of ZnO. Room temperature Hall measurements were performed to estimate the bulk concentration and results show that addition of rGO into ZnO matrix enhances the number of charge carriers. Thermopower measurements were carried out using differential dc method and a large reduction in Seebeck coefficient is observed.