Provided is a surface treatment method for a water-absorbent resin having excellent production efficiency, absorption capacity against pressure, fluid permeability or the like. Provided is a method for the surface treatment of a water-absorbent resin which comprises a) a step for mixing 0.1 to 20 parts by weight of an acid group-containing radically polymerizable compound and 5 to 20 parts by weight of water, relative to 100 parts by weight of a water-absorbent resin; and b) a step for polymerizing the acid group-containing radically polymerizable compound, wherein neutralization ratio of the acid group-containing radically polymerizable compound is 0 to 60% by mol, and is lower than neutralization ratio of the water-absorbent resin.