In this article, Ag nanoparticles (NPs) were easily loaded onto magnetic material through a tannic acid-metal polymer (PTA) intermedia layer to synthesize Fe304@PTA@Ag magnetic composite and the potential application as bactericidal agent for water disinfection was investigated. The as-obtained composite, with a Fe3O4 core of 150 nm, has plenty of Ag NPs of 15 nm adhered onto the PTA layer outside the core. The PTA layer, like the famous polydopamine complex, possesses excellent adhesive capacity to load more Ag NPs tightly and has specific antibacterial activity due to the numerous catechol groups. Therefore, remarkable bactericidal activity was achieved and 31.25 mg L-1 of Fe3O4@PTA@Ag disinfectant could inactivate more than 99% of the tested strains within 60 min. At the same time, the catechol groups also endow the PTA layer with reduction ability so that additional reductant is unnecessary during the formation of Ag NPs and the PTA complex can be fabricated much more rapidly. As a result, the magnetic composite can be synthesized simply with less cost. Moreover, the composite has a high magnetic saturation value of 55.47 emu g(-1) owing to the Fe3O4 core and the magnetic separation ability can play an important role in the recovery of the disinfectant. (C) 2017 Elsevier B.V. All rights reserved.