SnNb2O6 (BG = 2.3 eV) containing Sn2+ with a 5s(2) electron configuration showed the photocatalytic activity for H-2 evolution from an aqueous methanol solution under visible light irradiation (lambda > 420 nm) in the presence of a Pt cocatalyst. The energy structure calculation by the plane wave based density functional method revealed that the conduction and valence bands consisted of Nb4d and Sn5s orbitals, respectively. The valence band level consisting of the Sn5s orbitals was more negative than that consisting of O2p orbitals resulting in SnNb2O6 being responsive to visible light.