PURPOSE: To provide the titled water-dispersible resin which is obtd. from a vinyl group-contg. monomer, has a specified quotient of degree of dispersion, a specified gel content and a specified tensile strength, gives a cataplasm which has excellent initial tack and can retain excellent tack over a long period of time and in which drugs do not ooze out from ointment.

CONSTITUTION: The titled water-dispersible resin is obtd. from a vinyl group- contg. monomer and controlled to have a quotient of degree of dispersion of 1.5W7.0, a gel content of 10W90% and a tensile strength of 0.3W10kg/cm2. Generally, the water-dispersible resin is used under conditions of a solid content (JIS K-6828) of 10W70%, a viscosity (pH type rotational viscometer, 20r.p.m. at 25°C) of 10W30,000cP, a pH of 2W10 and a tack of 3W20. Examples of the vinyl group-contg. monomers are vinyl ester monomers having a 4W8C alkyl group as a side chain, (meth)acrylate ester monomers, fumarate esters, etc.