Provided are: a water-absorbing resin which, when used as an absorbent, retains a high water-absorbing ability and has such a property that the liquid to be absorbed is highly diffusible therethrough and can be inhibited from oozing out backward； and an absorbent article formed using an absorbent including the water-absorbing resin. The water-absorbing resin according to the present invention is a water-absorbing resin obtained by polymerizing a water-soluble ethylenic monomer in the presence of an internal crosslinking agent and thereafter crosslinking the polymer with a post-crosslinking agent, characterized in that when subjected to a liquid flow test, the water-absorbing resin has an effective absorbent index (K) indicated by equation (I) of 250 or greater. Effective absorbent index (K) = [(liquid flow amount) (g)]×[(artificial-urine absorption ratio) (g/g)] (I)
