This invention is to provide a method for surface-treatment of a water absorbent resin excelling in water absorption properties. This invention relates to a method for the surface-treatment of a water absorbent resin, which comprises: a) mixing 100 parts by weight of a water absorbent resin, 0.01-20 parts by weight of at least one radical polymerization initiator selected from the group consisting of persulfates, hydrogen peroxide, and azo compounds, and a radically polymerizing compound and b) irradiating the resultant mixture with active energy rays. The treatment particularly exalts the absorption ratio against pressure and the saline flow conductivity.