Catalytic activity was measured for the partial oxidation of toluene to benzaldehyde on potassium-promoted vanadium pentoxide catalysts. In addition, the surface acidity of these solids was inferred from the 2-propanol decomposition reaction, which gives an indication of the acid strength. The results of this work showed that both toluene conversion and selectivity to benzaldehyde are related to the presence of acidic sites in the catalyst.