Polyacrylic acid (salt) water-absorbent resin, production process thereof, and acrylic acid used in polymerization for production of water-absorbent resin

The present invention allows for the production, with a high productivity, of a water-absorbent resin having an improved relationship between absorption capacity and water-soluble polymer, which are conflicting properties of the water-absorbent resin, being easily controlled for polymerization reaction, being of no odor, being less colored, and being of high absorption properties (high absorption capacity under load and high PPUP). In a process for producing a water-absorbent resin by polymerizing an acrylic acid composition including acrylic acid and/or its salt, the process includes: (a) the step of carrying out radical polymerization of the acrylic acid composition to form a hydrogel crosslinked polymer; and (b) the step of drying the hydrogel crosslinked polymer by application of heat, the acrylic acid composition having an unpolymerizable organic compound content of 1 to 1000 ppm by weight, wherein the unpolymerizable organic compound has a solubility parameter of (1.0 to 2.5)*10 (Jm-3) 1/2.