Decorating ZnO with nanosheets of MoS2—a transition metal dichalcogenide characterized by a relatively narrow band gap—is a promising way to increase the photocatalytic activity of ZnO. However, limited studies report the effect of the layer number of of MoS2 nanosheets on the photocatalytic performance of ZnO/MoS2. In this work, ZnO nanorods were decorated with multilayer and few-layer (~11 and ~3 atomic layers) MoS2 nanosheets exfoliated for 4 h and 8 h, respectively. This type-II heterostructures were subsequently used as photocatalysts for the degradation of methyl blue. Our results show that the photocatalytic efficiency of the ZnO/MoS2 was less than that of pristine ZnO and it further decreased by 11% with increasing the number of layers and length of the MoS2 nanosheets. This effect may be due to the decrease of adsorption capacity of the water molecules on the ZnO/MoS2 system as indicated by the increasing contact angle from 17o–23o to 73o–76o. The increase in contact angle for ZnO/MoS2 could be due to the hydrophobic nature of the basal plane of the 2H-MoS2 phases, which are called inactive catalytic sites.