To provide a jellylike inorganic antimicrobial agent easily diffusible into a resin composition and excellent in weather resistance and antimicrobial property, and to provide its producing method.

This jellylike antimicrobial agent, into which there are diffused inorganic oxide particles comprising an antimicrobial metal component with a mean particle size of ≤500 nm, is obtained by adding a gelling agent to a colloid solution into which the inorganic oxide particles as mentioned above are diffused and then gelatinizing it.