[Problem] To provide: a zinc oxide powder having an average particle diameter of 1.1 µm or more and having an anti bacterial activity an anti bacterial agent comprising the zinc oxide powder and an anti bacterial composition containing the anti bacterial agent. [Solution] A surface treated zinc oxide powder which has an average particle diameter of 1.1 µm or more and of which the surface is treated with at least one compound selected from silicon oxide a silicone oil an organosilicon compound and an organotitanium compound.
