Provided is a method for producing water-absorbent resin including a polymerization step of polymerizing a polymerizable component containing a water-soluble ethylene unsaturated monomer solved in water by using a water-soluble azoic radical polymerization initiator, to obtain a reaction system containing a water-absorbent resin precursor, and a dehydration step of removing water from the reaction system by heating. In the dehydration step, the water-soluble radical polymerization initiator is added into the reaction system in an arbitrary first dehydration stage in which a water residual ratio calculated by formula (1) is 50% or more, and a reducing material is added into the reaction system in an arbitrary second dehydration stage in which the water residual ratio is lower than that of the arbitrary first dehydration stage by 10% or more. By this producing method, it is possible to produce a water-absorbent resin showing a good water-absorbent ability with the content of residual monomer being restricted. water residual ratio = (mass of water remaining in reaction system) / (mass of water-soluble ethylene unsaturated monomer used in polymerization step) * 100 (1)?
