H2C = C(R1)-COOR2 (1), wherein R1 represents hydrogen or methyl, and R2 represents hydrogen or C1-C4 alkyl, in the presence of polyvinyl alcohol and/or a derivative thereof and (B) at least one compound selected from the group consisting of (B-1) polyhydric alcohols, (B-2) esters of polyhydric alcohols and C1-C5 carboxylic acids, and (B-3) esters of polyvalent carboxylic acids and C1-C5 alcohols. The capsule of the present invention has excellent mechanical strength, while maintaining low moisture content, and thus exhibits excellent physical stability even when filled with a poorly soluble drug-dissolving solvent.
