An aqueous resin composition satisfying the following criteria (I)-(III). When this aqueous resin composition is used to treat fibrous sheets, it gives fibrous products having excellent performance and durability without any problem regarding safety, hygiene or pollution, and in particular, when it is used as a back coating resin for a separable fastener, a separable fastener is obtained having excellent resistance to fiber dropout in washing and resistance to chlorine bleaching agents, together with good durability over very long periods of use. (I) The aqueous resin composition essentially comprises (a) an aqueous dispersion of a polyurethane resin obtained from a macromolecular polyol, organic polyisocyanate, chain extending agent and 2,2-dimethylolbutanoic acid as starting materials, and, if required, (b) an aqueous dispersion of an acrylic resin. (II) When the resin comprising this aqueous resin composition is essentially only a polyurethane resin, the inherent viscosity ( eta inh) of the polyurethane resin measured at a concentration of 0.5g/dL in dimethylformamide solution is in the range of 0.2 - 0.7 dL/g. (III) After this aqueous resin composition is dried, the elastic modulus at 25 DEG C of the film obtained by heat treatment at 80 DEG C for 8 hours is in the range of 8.0 x 10 - 5.0 x 10 Pa, and the elastic modulus at 80 DEG C thereof is 8.0 x 10 Pa or less.