To produce a rapidly soluble coating agent composition, rapidly soluble at normal temperatures, hardly separating a pigment and capable of forming a film by coating thereof on a tablet such as a medicine.

This coating agent composition is obtained by adding and mixing a powdery pigment with a coating base while spraying a liquid plasticizer thereon. The coating base is a granular hydroxypropyl methyl cellulose or methyl cellulose having 200-1000μm average grain diameter and has ≤30wt.% concentration of grains having ≤75μm grain diameter. A polyethylene glycol having 190-630 weight average molecular weight is preferred as the plasticizer and blended in an amount of 5-30wt.% based on the coating base. Titanium oxide or an iron oxide or both are used as the pigment and blended in an amount of 1-30wt.% based on the coating base. The viscosity of a 2wt.% aqueous solution of the coating base is preferably 2-60cP. An aqueous coating solution can rapidly be prepared without requiring a special dissolving apparatus and a constant color tone can always be reproduced.