Ag-bearing particles for use in water sterilization, comprising particles consisting of garnet or composed mainly of garnet and, borne on the surfaces thereof, silver. A preferred aspect of silver is such that as shown in an SEM photograph given as a representative figure, particulate agglomerates of silver in groups are continuously or discontinuously borne on the surfaces of garnet particles. Efficient production of these particles can be accomplished by an electroless plating process wherein garnet particles are immersed in a mixed solution consisting of a reducing solution having at leastany of potassium sodium tartrate, glucose and acetaldehyde as a reducing agent dissolved in water, mixed with an aqueous silver nitrate solution and an ammonia solution.