To provide a method for producing a water absorbing resin, capable of producing the resin having low contents of a residual monomer and water-soluble matter, without being affected by a polymerization procedure.

This method for producing the water absorbing resin includes a process using an acrylic monomer (A) which contains an acrylic acid salt in an amount of at least 50 mol% based on a number of moles of the acrylic monomer (A) and has a content of a dimer acid (salt) of not more than 0.5 wt% based on a weight of the monomer (A) and polymerizing the monomer (A) in such a state that a content of iron atom in a polymerization liquid is not more than 5×10-6 wt% based on a weight of the monomer (A). The water absorbing resin produced by the method is useful for sanitary goods, such as a paper diaper, a sanitary napkin, and a medical blood holding agent. Further, the resin is used for a pet urine absorbing agent, a urine gelling agent for a portable toilet, a freshness keeping agent for a vegetable, a fruit, etc., a drip absorbing agent for meet and fishery products, a cold reserving agent, a disposable pocket warmer, a gelling agent for a battery, a water holding agent for a plant, soil, etc., a dew condensation preventing agent, a water stopping agent, a packing agent, artificial snow, etc.