The theoretical study on the mechanism of butane oxidation using model complexes of vanadyl pyrophosphate has been investigated using density functional theory (DFT) method. The monomeric complex VO(OH)(2)(OH2)(2) was selected as a fundamental structure. The complexes bearing one phosphoric residue were selected for clarifying the effect of pyrophosphoric moieties on the catalyst. The complexes having two vanadium units were selected as two-layer models of the catalyst for clarifying the influence of the presence or absence of lattice oxygen and the effect of the oxidation states of the inner vanadium atom. The introduction of a phosphoric moiety on one of the hydroxy groups strongly stabilizes the lower oxidation states of the complexes. This result suggests that the surface vanadium species having the higher 5+ oxidation state should possess stronger oxidation ability. The presence of the vanadium (4+) atom at the lower layer relatively destabilizes the V3+ state of the upper vanadium complexes, and stabilizes the peroxo-vanadium (4+) complexes, which suggests that the lattice oxo-oxygen in vanadyl pyrophosphate may play an important role in the activation of molecular oxygen.