Abstract: In this study, g-C3N4 is synthesized by direct calcination of urea. XRD, DRS was used to characterize its property. Degradation of Rhodamine B by g-C3N4 activated sodium persulfate under visible light is investigated. The dosage of g-C3N4, sodium persulfate in the degradation process was also studied. Results showed that 91.67% of RhB was degraded in 30 min by g-C3N4 activated sodium persulfate under visible light. A positive correlation existed between degradation ratio of RhB and amount of g-C3N4 or sodium persulfate. The results of titration experiment indicate that g-C3N4 is effective for activation of sodium persulfate under visible light. Moreover, g-C3N4 shows good stability after four cycle experiments.