Graphene/Bi2WO6 composites have been synthesized by hydrothermal reduction at 160°C for 24 h using ethanol as the reducing agent. All as-prepared composites were characterized using X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption, and photocatalytic activity evaluation. The effective charge separation of graphene/Bi2WO6 composites was caused by the electrical conduction of graphene which is the most important factor. The results have proved the formation of interfacial contact between graphene nanosheets and Bi2WO6 nanoplates. The adsorptivity for azo dyes was enhanced greatly with the introduction of graphene. The oxy-functional groups located at the edges of graphene were responsible for the enhanced adsorptivity. As-prepared graphene/Bi2WO6 composites exhibited enhanced light absorption from UV to visible-light region. In addition, the introduction of graphene would also result in smaller crystalline size and lower crystallinity of Bi2WO6. Graphene/Bi2WO6 composites containing an appropriate amount of graphene were proved to exhibit higher adsorptivities and photocatalytic activities for azo dyes. High photocatalytic activities of graphene/Bi2WO6 composites were considered to be the synergetic effects of high adsorption, high light absorption, and high electrical conduction induced by the introduction of graphene.