Fe5(PO4)4(OH)3·2H2O has been successfully synthesized by a simple hydrothermal process. The effects of hydrothermal temperature and pH value on the morphologies and sizes of the Fe5(PO4)4(OH)3·2H2O particles were investigated. The Fe5(PO4)4(OH)3·2H2O photocatalyst showed lower photocatalytic activity for the degradation of methylene blue under visible light irradiation. But the heterogeneous Fenton-like Fe5(PO4)4(OH)3·2H2O with H2O2 showed highly efficient photocatalytic activity in the photocatalytic decomposition of methylene blue. Effective electron transfer from the visible light-excited dyes to Fe(III), which leads to regeneration of Fe(II) and an easy cycle of Fe(III)/Fe(II), results in much faster degradation and mineralization of methylene blue in the photo-Fenton reaction under visible light irradiation.