A hydroabsorbent resin prepared by inverse phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent and at least one azo compound and a peroxide and performing post-crosslinking with a post-crosslinking agent in the presence of water in a range 1 to 400 parts by mass based on 100 parts by mass of the water-soluble ethylenically unsaturated monomer； wherein the amount of the internal crosslinking agent used is 0.000001 to 0.02 mol, based on 1 mol of the water-soluble ethylenically unsaturated monomer； the amount of the post-crosslinking agent used is 0.00001 to 0.01 mol, based on 1 mol of the total amount of the water-soluble ethylenically unsaturated monomer； the post-crosslinking agent is at least one selected from the group consisting of diglycidyl ether of (poly) ethylene glycol, diglycidyl ether of (poly) glycerin, triglycidyl ether of (poly) glycerol, triglycidyl ether of trimethylolpropane, polyglycidyl ether of (poly) propylene glycol and polyglycidyl ether of (poly) glycerol； and wherein the hydroabsorbent resin satisfies all of the following properties: (A) a physiological saline hydroabsorption capacity of 55 g / g or more, a physiological saline hydroabsorption capacity under a 4.14 kPa load of 15 ml / g or more, and a residual monomer content of 300 ppm or less； and (B) a yellowness index of 5.0 or less and a ratio of the yellowness index change (ΔYI) after leaving for 10 days under 70 ° C and 90% RH of 10 or less.Una resina hidroabsorbente preparada mediante polimerización en suspensión en fase inversa de un monómero etilénicamente insaturado hidrosoluble en presencia de un agente de reticulación interna y al menos un compuesto azoico y un peróxido y realizando una posreticulación con un agente de posreticulación en presencia de agua en un intervalo de 1 a 400 partes en masa basado en 100 partes en masa del monómero etilénicamente insaturado hidrosoluble； en donde la cantidad
