To provide an adhesive which has various kinds of excellent dispersion stability and gives fiber products, such as nonwoven fabrics or impregnated paper, having excellent wet strengths.

This adhesive for treating fibers comprises the emulsion of a homopolymer comprising one kind of monomer units selected from the group consisting of acrylic ester-based monomer units, methacrylic ester-based monomer units, aromatic vinyl-based monomer units and conjugated diene-based monomer units or a copolymer containing one or more kinds of monomer units selected from the monomer unit group as a main component. The emulsion is dispersed and stabilized with a water-soluble polymer compound which contains alcoholic hydroxy groups and a weight-average mol. wt. of ≥2,000. Therein, at least a part of the water-soluble polymer compound which contains alcoholic hydroxyl group is grafted to the homopolymer or copolymer in a grafting rate of 0.5 to 30 wt.%.