Fe₂(MoO₄)₃ microspheres were synthesized by a hydrothermal method. The Fe₂(MoO₄)₃ microspheres showed highly efficient photocatalytic activity for the degradation of methylene blue under visible light irradiation. Kinetic studies using radical scavenger technologies suggested that holes were the dominant photo-oxidants. On the basis of the experiment results, the difference in photocatalytic activities of the Fe₂(MoO₄)₃ samples were mainly attributed to the defects, which could act as inactivation centers, reducing the total photocatalytic activity significantly.