PURPOSE: To obtain a polymer having improved absorption amount, absorbing rate, gel strength in swelling, etc., by polymerizing a hydrophilic monomer in the presence of specific amounts of a polymerization initiator and a crosslinking agent, adjusting the water content of the prepared polymer to a specific range and crosslinking again.

CONSTITUTION: A carboxyl or carboxylate group-containing water-soluble polymerizable monomer (e.g. acrylic acid, etc.) is polymerized and crosslinked in the presence of both (A) 0.01W0.15mol% based on the monomer of a water-soluble radical polymerization initiator (e.g. sodium persulfate, etc.) and (B) 2×10-3W8×10-2mol% based on the monomer of a polyglycerol chain-containing crosslinking agent (e.g. polyglycerol polyacrylate, etc.) or a polyoxyalkylene chain-containing crosslinking agent having 3W200 oxyalkylene units on the average, the prepared polymer is adjusted to 10W40wt%, especially 15W35wt% water content and the polymer is further crosslinked by the use of (C) a water- soluble crosslinking agent (e.g., polyglycidyl ether, etc.) containing two or more reactive crosslinking groups.