BaBi0.53+Bi0.55+O3 (BBO) with an ordered arrangement of Bi3+ and Bi5+ in the crystal lattice was studied for its photocatalytic activity with a view to understand the role of valency ordering. The visible light photocatalytic activity of BBO towards 4-chlorophenol degradation decreased with La3+ substitution. The calculated density of states of BBO showed a decrease in the valence band width with La3+ substitution. The valency ordering of Bi3+ and Bi5+ and the concomitant charge transfer between them are vital in the photocatalytic activity of BBO. La3+ substitution in the lattice reduces the photocatalytic activity by hindering the charge transfer process. (c) 2007 Elsevier B.V. All rights reserved.