This invention relates to a water-absorbent resin of new, novel type obtained from polymerization of a water-soluble ethylenically unsaturated monomer followed by surface treatment and, in addition, a process for producing this resin. The water-absorbent resin in this invention has average particle diameter in a specially defined range and a narrow range of particle distribution. And furthermore, since the particle surface is treated with crosslinking, a balance is very good among water absorption properties, for example, between water absorption capacity and water absorption rate, and between gel strength and suction force. This water-absorbent resin is takable a angle-lacking, non-sphere shape and in a case of this type of shape, it is superior in such handling properties as falling off from an basis material being hard.; Since the production process in the present invention comprises crosslinking treatment for the particle surface of a specially defined water-absorption polymer, the crosslinking is performed with good efficiency and, a water-absorption resin being superior in a balance among water absorption properties is obtainable with an economic advantage.; This specially defined water-absorption polymer particle is obtained by polymerizing a water-soluble ethylenically unsaturated monomer in a process of reverse-phase suspension polymerization, In the production process of this invention, since the aqueous monomer solution is chosen from those in a specially defined viscosity range and then, dispersed and suspended by using a specially defined dispersing agent, a specially defined water-absorbent resin is easily obtainable wherein, not only the average particle diameter is controlled by adjusting the viscosity of an aqueous monomer solution, but also the particle diameter distribution resulted is narrow. In this production process, the particle shape can be changed by changing up and down the viscocity of an aqueous solution of monomer in the above-described specially defined range.; The water-absorbent resin in this invention, because it has the above-described properties, is preferably used for sanitary materials and the like.