PURPOSE: To obtain the title composite material excellent in water absorptivity, safety, easiness of handling and useful for paper diapers, etc., by applying an aqueous solution of a specified polymerizable monomer to a fibrous base, polymerizing it in the presence of a radical initiator and heating the obtained composite material.

CONSTITUTION: An aqueous solution (concentration ≥ 30 wt%) of 1W10,000 pts.wt. polymerizable monomer (B) based on acrylic acid neutralized to such a degree that at least 20% of its carboxyl groups are in the form of an alkali metal salt or an ammonium salt is applied to 100 pts.wt. fibrous base (A) comprising a cellulosic fiber and/or a polyester fiber and being in the form of loose pad, carded web, paper, (non)woven fabric, knitted fabric or the like, and polymerized in the presence of a water-soluble radical polymerization initiator to obtain a composite material comprising component A and a component B- derived polymer and containing below 40 pts.wt. water per pt.wt. component A. this composite material is heated to 100W250°C to obtain the title composite material having a content of unpolymerized monomer lesser than that of the starting composite.