A novel magnetic epigallocatechin-3-gallate-modified Fe3O4 nano-catalyst (EGCG@Fe3O4) was fabricated, characterized, and tested to active peroxymonosulfate (PMS) for the degradation of sulfadiazine (SD) in solution. The results illustrate that EGCG@Fe3O4 exhibits a higher catalytic ability than unmodified Fe3O4 toward SD degradation. Both SD removal and PMS decomposition clearly follow the pseudo-first-order kinetic pattern in the EGCG@Fe3O4/PMS system. When the catalyst and PMS dosages were 0.8 g/L and 0.3 mM, respectively, the pseudo-first-order rate constants (k(obs)) were 5.41 x 10(-2) and 1.0(5) x 10(-2) min(-1) for the EGCG@Fe3O4/PMS and Fe3O4/PMS systems, accompanied by 97.9% and 51.4% utilizations of initial PMS, respectively. Numerous hydroxyl radicals ((OH)-O-*) and few sulfate radicals (SO4*-) were measured in the EGCG@Fe3O4/PMS system by in situ electron spin resonance (ESR) spin-trapping techniques. The production of reactive radicals most likely involved the activation of PMS by the cycle of Fe2+-Fe3+ on the EGCG@Fe3O4 catalyst surface, with EGCG enhancing the redox of Fe3+ to Fe2+ significantly. The EGCG@/PMS system may provide new insights for the decomposition of organic pollutants dissolved in water.