PURPOSE: To obtain a water-absorptive material excellent in water absorption, speed of water absorption, and safety by irradiating water-absorptive resin particles agglomerated in plane form with actinic radiation.

CONSTITUTION: Water-absorptive resin particles (e.g. particles of a poly(meth) acrylic acid or poly(meth)acrylamide) agglomerated in plane form are irradiated with actinic radiation (e.g. ultraviolet rays, electron beams or radiation). It is desirable to obtain the water-absorptive resin particles agglomerated in plane form through the step of casting a particulate water-absorptive resin into a plane form with a thickness of about 0.3-5 mm on a support and the step of adding at least one of water and steam in an amount of 10-150 pts.wt. based on 100 pts.wt. water-absorptive resin [or adding water and polyhydric alcohol (e.g. ethylene glycol) respectively in amounts of 3-30 pts.wt. and 5-50 pts.wt. based on 100 pts.wt. water-absorptive resin] while keeping the state of a plane obtained in the first step.