Cobalt-mediated peroxymonosulfate (PMS) activation is an effective way to generate sulfate radicals for the degradation of pollutants. Herein, a heterogeneous Co-based catalyst was prepared by integrating the cobalt species to the cavities of g-C(3)N(4 )via the Co-N bonds through the methods of impregnation and calcination, which was applied to activate PMS for the degradation of organic contaminates under visible light. The cobalt species were atomically dispersed on g-C3N4, which could provide more reactive sites for PMS activation. The catalytic efficiency of cobalt-doped g-C3N4 was greater than that of pure g-C3N4 or even slightly higher than that of the homogeneous cobalt ions during the photo-assisted PMS activation catalytic processes. The optimum Co loading is 1.0% in weight. In 25 min, the dye of rhodamine B was almost completely degraded with a 70.5% of total organic carbon (TOC) removal under its natural pH value in the presence of such catalytic system. The enhanced catalytic activity of Co-doped g-C3N4 was due to the effective separation of the photo-generated charges as well as the sufficient accessible reactive sites for PMS activation. And the synergistic interaction between the photocatalytic and PMS activation processes facilitated the generation of active species for the removal of pollutants.