Uniform two-dimensional MoS2 nanoflakes were vertically assembled on the surface of reduced graphene oxide (MoS2/rGO composite film) via a hydrothermal process. The structure, morphology and optical properties of MoS2/rGO composite were studied. It is demonstrated that photocatalytic activity of the composite films for the degradation of methylene blue in the visible light range is much higher than that of isolated MoS2 and rGO. This is associated with an efficient transfer and a rapid separation of photogenerated electrons and holes at the heterojunction between MoS2 nanoflakes and rGO film.