Disclosed is a polyvinyl alcohol aqueous dispersion having excellent storage stability which is capable of forming a coating film with excellent water resistance and transparency even when it is dried at room temperature. Also disclosed are a composition and a coating agent for paper. Specifically disclosed is an aqueous dispersion of a resin which is composed of a polymer containing at least 20 weight % of a vinyl monomer unit (A) having an epoxy group and a vinyl alcohol polymer (B) while having a weight ratio (A)/(B) of 2/100-200/100. The weight ratio of (A) bonded to (B) is not less than 50% relative to the total weight of (A), and the average particle size of the resin determined by dynamic light scattering is not more than 500 nm.