Mesoporous graphitic carbon nitrides were synthesized by a thermal-induced polymerization of NH4SCN on the surface of silica nanoparticles as the templates. The catalysts thus obtained were used as visible light photocatalysts for the degradation of organic pollutants in water. The physicochemical properties of catalysts were characterized by several techniques. The photocatalytic activity of samples was evaluated by the decomposition of chlorophenol and phenol in aqueous phase. Results demonstrated that mesoporous graphitic carbon nitrides can photocatalytically oxidize and eventually mineralize organic pollutants in aqueous solution under visible light irradiation. The photocatalysts can induce the formation of reactive oxy-species such as H2O2, ˙OH and ˙O2−/˙OOH under visible light irradiation, while keeping a high photocatalytic reactivity during recycling operations. The higher activity of mesoporous carbon nitrides compared to nonporous carbon nitride can be attributed to their enlarged surface area and enhanced light-harvesting effect, facilitating the photogeneration of active oxy-radicals in water.