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 there through 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 cross linking 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)
