Electrolytes play a crucial role in the storage and conversion of energy in a vanadium redox flow battery（VRFB）. As an important transport property, the viscosity of electrolyte provides information of inter-particle interactions and solution microstructure. This is of significance to the optimization of the overall performance of the VRFB. We measured the viscosity and density of aqueous based VOSO4 solutions in a concentration range of 0.5-3.0 mol/kg at 283.15-323.15 K, calculated the activation energy associated with the viscous flow. Based on Eyring＇s theory, a semi-empirical equation was proposed for the viscosity prediction. Such a relationship agreed well with the experimental data within 0.3%.