In this paper, a plasmonic Ag/AgBr heterostructure was reduced by AgBr, which was successfully synthesized by a facile hydrothermal process at a temperature as low as 90 degrees C. The morphological and structural observation, crystallinity and optical performance of the products grown were carried out by using scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry and UV-vis diffuse reflectance spectroscopy. The photocatalytic activities of Ag/AgBr heterostructures were evaluated by the degradation of methylene blue under 450 nm LED arrays. The results revealed that the plasmonic Ag/AgBr heterostructures exhibited much higher photocatalytic activities than pure AgBr and commercial Degussa P25. The visible-light photocatalytic activity enhancement of Ag/AgBr heterostructures could be attributed to the surface plasmon resonance and its synergistic effect on the photosensitive AgBr. Furthermore, a mechanism of the plasmon synergistically enhanced photocatalytic process was proposed.