Photocatalytic degradation of methylene blue (MB) dye was first investigated over the CaIn2O4 photocatalyst under visible light irradiation. MB was degraded largely after visible light irradiation for 120 min over the photocatalyst at room temperature in air. The high activity could be kept in a wide range of wavelength up to 580 nm. SO42- concentration was detected as a product of MB degradation, indicating that MB was mineralized over the CaIn2O4 photocatalyst under visible light. The photocatalytic reaction pathway of MB degradation over the photocatalyst was also suggested. (C) 2003 Elsevier B.V. All rights reserved.