Three kinds of Ag3PO4-AgX (X = Cl-, Br- and I-) were prepared by the co-precipitation method between AgNO3 and Na2HPO4 + KX (X = Cl-, Br- and I-) solutions. Their photocatalytic activities were also investigated by decolorization of a methylene blue solution. Under visible light irradiation, photocatalytic decolorization of the dye using Ag3PO4-AgX as photocatalyst could occur by interaction between a hole in the valence band of the photocatalyst and the methylene blue dye molecules as it cannot detect the emission of 7-hydroxylcoumarin. AgCl and AgBr induce the Ag3PO4 to increase its photocatalytic decolorization efficiency. On the other hand, the compound Ag3PO4-AgI also showed a high adsorption for methylene blue in the dark. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.