The present invention provides a powdery starting material for preparing a drug-coating solution, which has high safety as a drug component and is very rapidly dissolved in room temperature water upon preparation of a coating solution. The powdery starting material for preparing a drug-coating solution comprises hydroxypropylmethyl cellulose and/or methyl cellulose particles having an average particle size ranging from 200 to 1000 .mu.m and whose content of particles having a particle size of 75 .mu.m or smaller is not more than 30% by weight. More preferably, the viscosity of a 2% by weight aqueous solution of the powdery starting material as determined at room temperature ranges from 2 to 60 cP and preferably 2 to 20 cP.