PURPOSE: To obtain an admixture for mortar having excellent adhesion, durability and mechanical strength, a polymer cement mortar composition containing the admixture and a constructional joint material having excellent adhesion.

CONSTITUTION: An admixture for cement mortar comprises (A) an aqueous emulsion obtained by subjecting an ethylenic unsaturated monomer such as vinyl acetate to emulsion polymerization in the presence of a carboxyl group modified polyvinyl alcohol such as itaconic acid-modified polyvinyl alcohol and (B) a polyamide-based resin such as polyamidoepichlorohydrin. A constructional joint material for cement mortar is composed of (A) the aqueous emulsion and (B) the polyamide-based resin. A polymer cement mortar composition consists of an aqueous substance and the admixture for cement mortar as main components.