It is possible to improve the gel shape stability of the absorber, and provide an absorbent resin having excellent water absorption performance.The water absorbent resin of the present invention is a polymer of water-soluble ethylenically unsaturated monomer, and has the following characteristics (1) and (2).(1) the amount of collapse at 20 times swell is 30 mass% or less.(2) the amount of dissolved salt is 25 mass% or less.(measuring method of collapse quantity at 20 times swelling)5 g of water absorbent resin is added to 100 g of the physiological saline, and the saline is absorbed in the absorbent resin to obtain the gel.The resultant gel is formed into a cylindrical shape having a length of approximately 3.6 cm and a radius of 2.8 cm, respectively.The mass of the five cylindrical gels formed is measured, and three gels excluding the heaviest and the lightest ones are used as samples.After measuring the mass wa (g) of each sample, a mass measuring sample was placed on the top sieve of the standard standard sieve of 5.6 mm sieve and the receiver plate, and the low tap vibrator (rotational speed 290 rpm, impact number 165 RPM) was vibrated for 10 minutes and passed through the sieve The mass WB (g) is measured.The decay amount of the sample is calculated from the following equation.Sample collapse (WB) / WB (g) / wa (g) x 100The average value of the amount of collapse for three samples to be measured is assumed to be the amount of collapse of the absorbent resin at the time of swelling of 20 times.吸収体のゲル形状安定性を向上させることができ、優れた吸水性能を備える吸水性樹脂を提供する。 本発明の吸水性樹脂は、水溶性エチレン性不飽和単量体の重合体であって、下記（１）及び（２）の特性を備える。（１）２０倍膨潤時の崩壊量が３０質量％以下である。（２）生理食塩水に対する溶解量が２５質量％以下である。（２０倍膨潤時の崩壊量の測定方法） 生理食塩水１００ｇ中に吸水性樹脂５ｇを加え、吸水性樹脂に生理食塩水を吸収させてゲルを得る。得られたゲルを、略均等に５分割し、それぞれ、長さ３．６ｃｍ、半径２．８ｃｍの円筒形の型に入れて成形する。成形された５つの円筒形のゲルの質量を測定し、最も重いものと最も軽いものを除いた３つのゲルを試料とする。各試料の質量Ｗａ（ｇ）測定した後、ＪＩＳ標準篩の目開き５．６ｍｍ篩と受け皿の順に組み合わせた最上の篩に、質量を測定した試料を入れ、ロータップ式振とう器（回転数２９０ｒｐｍ、衝撃数１６５ｒｐｍ）を用いて１０分間振とうさせて、篩下に通過した質量Ｗｂ（ｇ）を測定する。試料の
