Provided are: a water-absorbent resin which has a better water absorption performance and with which it is possible to improve absorption performance under a load when used in an absorbent material and an absorbent article using an absorbent material that includes the water-absorbent resin. This water-absorbent resin, obtained by polymerising a water soluble ethylenically unsaturated monomer in the presence of an internal-crosslinking agent and by post-crosslinking using a post-crosslinking agent, has a water-absorption capacity of physiological saline under a load of 4.14 kPa of 16 mL/g or more, has a mass proportion of particles from 150 to 850 µm relative to the whole proportion of 85 mass% or more, moreover has a mass proportion of particles from 300 to 400 µm relative to the whole proportion of 20 mass% or more, and has an absorption capacity elasticity index represented by formula (I) of 68,000 or more. Absorption capacity elasticity index = storage elastic modulus [Pa] × centrifugal retention rate [g/g] ...(I)
