Provided is a water-absorbent resin that increases the diffusivity of a to-be-absorbed liquid and that makes it possible to effectively decrease the amount of re-wet. The water-absorbent resin is obtained by polymerizing a water-soluble ethylenicallyally unsaturated monomer under the presence of an internal-crosslinking agent, has the water-absorption capacity of physiological saline under a load of 4.14 kPa at 120 minutes passed from the start of water absorption of 20 ml/g or more, and exhibits the degree of swelling under a load at 30 minutes of 70% or less when the water-absorption capacity of physiological saline under a load of 4.14 kPa at 120 minutes from the start of water absorption is designated as the degree of swelling under a load of 100%. The water-absorbent resin can be produced by performing the following steps in a method in which a water-absorbent resin is produced by performing reverse phase suspension polymerization of a water-soluble ethylenicallyally unsaturated monomer in a hydrocarbon dispersion medium under the presence of an internal-crosslinking agent: a step in which polymerization is performed under the presence of an azo compound and a peroxide and a step in which a water-containing gel obtained by said polymerization is post-crosslinked using a post-crosslinking agent.本發明提供一種吸水性樹脂,其能夠提高被吸收液的擴散性,而能夠有效地使回流量降低。本發明的吸水性樹脂,其是藉由使水溶性乙烯性不飽和單體在內部交聯劑的存在下進行聚合來獲得,其中,該吸水性樹脂在4.14kPa荷重下的生理食鹽水吸水能力,當從開始吸水經過120分鐘後,是20ml/g以上;並且,當將從開始吸水經過120分鐘後的在4.14kPa荷重下的生理食鹽水吸水能力設為荷重下膨潤度100%時,經過30分鐘後的荷重下膨潤度是70%以下。如此的吸水性樹脂,能夠藉由下述方法來製造:在內部交聯劑的存在下,使水溶性乙烯性不飽和單體在烴分散介質中進行反相懸浮聚合而得,其中,該製造方法具有以下步驟:在偶氮系化合物與過氧化物的存在下實行聚合的步驟;及,利用後交聯劑將由該聚合而得的含水膠體狀物進行後交聯的步驟。
