We have investigated the effect of the co-substitution of Sn-IV and Ni-II ions on the electronic structure and physicochemical property of InMO4 (M = Nb, Ta) semiconductors. The co-substitution leads to a red-shift of absorption edge as well as to an appearance of satellite peak below the absorption edge. Depending on the nature of valence orbitals, the substitution of p- and d-block elements results in the lowering of conduction band and the formation of impurity states in the middle of bandgap, respectively. Such a band modification makes the photocatalytic activity of InMO4 improved against the photodegradation of organic molecules. (c) 2006 Elsevier B.V. All rights reserved.