To provide a coating compsn. which causes no interference fringe on the surface of a plastic part, has good weather ability, and is free from an uneven reflected color by compounding a specified organosilicon compd. or a hydrolyzate thereof with composite fine particles of zinc antimonate.

The organosilicon compd. is one represented by the formula: R1aR2bSi(OR3)4-(a+b) (R1 represents a 4-14 C org. group having a functional group or an unsatd. double bond; R2 is a 1-20 C hydrocarbon group or a halogenated hydrocarbon group; R3 represents a 1-4 C alkyl, alkoxyalkyl, or acyl; a is 0 or 1; b is 0 to 2; and a+b is 0, 1 or 2) (e.g. γglycidoxypropyltrimethoxysilane). Zinc antimonate is composed mainly of antimony and zinc and takes a composite form wherein antimony and zinc are each combined with an oxygen atom. The fine particles are used in the form of a colloidal soln. thereof dispersed in water, an org. solvent, or a mixture thereof (particle diameter: 1 to 300nm). The thickness of the coating layer is pref. 0.05 to 30μm.