The present invention provides a coating agent for a pharmaceutical solidpreparation, which imparts an unpackaged pharmaceutical solid preparation withexcellentbarrier properties equivalent to those of a PTP sheet without affecting thedisintegrationproperties of the pharmaceutical solid preparation. Provided is a coatingagent for apharmaceutical solid preparation with comprises a polyethylene glycol havingan averagemolecular weight of 950 to 25,000 and a swelling clay, wherein the mass ratioof thepolyethylene glycol and the swelling clay is 2:8 to 6:4 and the mass ratio ofsaid swelling clayin a film formed on the surface of the pharmaceutical solid preparation is notless than 20%.
