Absorbent resin and method for producing the same

A water-absorbing resin comprising a water soluble unsaturated monomer having a dissociable group as a main component of a repeating unit of a main chain, wherein

• the water-absorbing resin has an internal crosslinked structure,
• a crosslinked structure index expressed by the following numerical formula 1 is 14 or more,
• a weight average molecular weight (Mw) of the water-absorbing resin after a hydrolysis treatment is 220,000 or less, and
• a molecular weight distribution (Mw/Mn) of the water-absorbing resin after a hydrolysis treatment is 1.00 or more and 3.40 or less:
• [Math. 1]
• Crosslinked structure index=(Equilibrium swelling capacity with respect to 0.9 wt % physiological saline solution)1/3/(Weight average molecular weight (Mw) after hydrolysis treatment)×1000000 [Numerical formula 1]
• where the hydrolysis treatment is a treatment to leave 50 mg of the water-absorbing resin as a solids content to stand still in 10 g of a 0.1 mol/l aqueous sodium hydroxide solution for 3 weeks at 80° C., and the weight average molecular weight (Mw) is a value measured after the treatment.