Benzene hydroxylation with hydrogen peroxide catalyzed by selectively site-substituted vanadium (V) polyoxometalates was classified into two reaction types based on the turnover vs. time curve with or without an induction period. A prototypic example was the catalysis by the two geometrical isomers of trivanadium-substituted Keggin-type polyoxotungstate; [alpha-1,2,3-SiW9V3O40](7-) with a longer induction period and [alpha-1,2,3-SiW9V3O40](7-) without an induction period, respectively. The V-51 NMR measurements showed that the former reaction was catalyzed by the vanadium species within the polyoxotungstate, whereas the latter was catalyzed by the vanadium species generated from the polyoxotungstate. This was the case for the catalysis by the previously reported polyoxometalates, i.e., [alpha-1,2,3-PW9V3O40](6-), [alpha-1,2-PW10V2O40](5-) and [alpha-PMo11VO40](4-). Also reported are the effect of the countercation on the catalysis by [alpha-1,2-PW10V2O40](5-) and [alpha-PMo11VO40](4-), and the effect of the used amounts of hydrogen peroxide. The reactions by the Keggin-type [alpha-1,4,9-PW9V3O40](6-), the two Dawson-type [alpha(2)-1,2-P2W16V2O62](8-) and [alpha(2)-P2W15Mo2VO62](7-) polyoxometalates showed turnover vs. time curves without an induction period. However, the P-31 and V-51 NMR spectra revealed that the reaction by [alpha(2)-P2W15Mo2VO62](7-) was catalyzed by the vanadium species within the polyoxometalates. As a model of the catalysis by oxovanadium species generated from polyoxometalates, the reactions using NaVO3 or Na3VO4 in water with varied pH were examined. Under the acidic conditions there was no induction period, while under the neutral conditions there was a distinct induction period. The V-51 NMR measurements showed that the reactive species participating in these two reactions were VO(O-2)(+) and VO(O-2)(2)(-), respectively.