The key to solving environmental and energy issues through photocatalytic technology requires highly efficient, stable and eco-friendly photocatalysts. Graphitic carbon nitride (g-C3N4) is one of the most promising candidates except for its limited photoactivity. In this work, a facile and scalable one-step method is developed to fabricate an efficient heterostructural g-C3N4 photocatalyst in situ coupled with MoS2. The strong coupling effect between the MoS2 nanosheets and g-C3N4 scaffold, numerous mesopores and enlarged specific surface area helped form an effective heterojunction. As such, the photocatalytic activity of the g-C3N4/MoS2 is more than three times higher than that of the pure g-C3N4 in the degradation of RhB under visible light irradiation. Improvement of g-C3N4/MoS2 photocatalytic performance is mainly ascribed to the effective suppression of the recombination of charge carriers.