BiFeO3 nanoparticles have been synthesized by hydrothermal method. Ag nanospheres (1 wt%) have been successfully decorated on the surface of BiFeO3 nanoparticles by photo-deposition method. XPS study confirms the decoration of Ag on the surface of BiFeO3. Synthesized nanoparticles have been characterized by studying their morphological, structural, optical and photocatalytic properties. It has been found that the photocatalytic properties of Ag decorated BiFeO3 nanoparticles to decompose methylene blue in visible light are far better than those of bare BiFeO3 nanoparticles. The mechanism of enhanced photocatalytic activities of Ag-decorated BiFeO3 nanoparticles has been disclosed.