When molybdophosphoric acid, H3PMo12O40, was treated with pyridine and heated in N-2 how at 420 degrees C as an optimized temperature, a black solid catalyst was formed with a structure of orthorhombic phase and in a reduced state. This reduced H3PMo12O40(PY) catalyst showed a high potentiality in the propane and isobutane oxidation with molecular oxygen to acrylic acid and methacrylic acid above 300 degrees C. It was proved that the higher the reduction degree of the catalyst is, the higher the oxidation activity and selectivity to partial oxidation products are. The FT-IR study revealed that, in the lattice of the heat-treated H3PMo12O40(PY) catalyst, pyridinium ion remained to assume the highly resistant orthorhombic secondary structure against reoxidation, and on the surface, Lewis acid sites were generated with the formation of the primary oxygen-deficient Keggin structure. A possible reaction mechanism was proposed for alkane oxidation, where protons and electrons in the reduced H3PMo12O40(PY) catalyst cooperate to activate molecular oxygen.