Process for improving granular detergents

A process for improving the properties of granular detergents, that is, caking preventability, fluidity and particle hardness, which comprises spray-coating a coating agent [I] consisting of the silicates, sulfates, carbonates and hydroxides of alkali metals and a coating agent [II] consisting of polyvalent metal sulfates separately onto a granular detergent obtained by the conventional spray granulating method, tumbling granulating method, piston granulating method, pressure granulating method and the like, under a condition in which the granular detergent is in a fluid state; causing a reaction on the surface of the granular detergent particles; and forming thereon a coating film of a water-insoluble or poorly water-soluble substance.