Provided are: a water-absorbent resin that has excellent water absorption performance and in which discoloration is minimized before and after long-term storage under high temperatures and high humidity and an absorbent article that uses the water-absorbent resin. The water-absorbent resin is obtained by polymerizing a water-soluble ethylenically unsaturated monomer under the presence of an internal crosslinking agent and using a post-crosslinking agent to post-crosslink the result. The water-absorbent resin satisfies the following properties: (A) the saline water absorption capacity is 55 g/g or more, the saline water absorption capacity under a load of 4.14 kPa is 15 ml/g or more, and the residual monomer content is 300 ppm or less and (B) yellowness is 5.0 or less and the rate of change (?YI) in yellowness after being left for ten days under an environment of 70 °C and 90% relative humidity is 10 or less.
