As 2-phenylbenzimidazole-5-sulfonic acid (PBSA) represents most-extensively used UV absorber, release of PBSA into the aquatic environment has posed huge risks to the ecology because PBSA is an endocrine disruptor and highly soluble in water. For developing effective approaches to eliminate PBSA from water, this study develops cobalt sulfide for the first time as a heterogeneous catalyst to activate monopersulfate (MP) for producing sulfate radical (SO4[rad]−) to degrade PBSA. In particular, a cubic bundle of cobalt sulfide nanoplates (CoSNP) is created from a convenient sulfurization of cobaltic metal organic framework (CoMOF) to convert this CoMOF to CoSNP. This resultant CoSNP can show much higher catalytic activities than the pristine CoMOF, and the reference catalyst, Co3O4 nanoparticle, for activating MP to degrade PBSA. With very low dosages of CoSNP = 25 mg/L and MP = 100 mg/L, 5 mg/L of PBSA can be completely removed in 45 min, proving that CoSNP is a promising catalyst for activating MP to PBSA. The activation mechanism and degradation pathway of PBSA degradation by CoSNP + MP is investigated here by electron paramagnetic resonance, and mass spectrometry to offer useful insights into degradation behaviors for developing sulfate-radical-based processes of PBSA degradation using cobalt sulfide catalysts.