To obtain a radio wave absorber capable of exhibiting stable absorbing characteristics, without the need of any complicated process control by mixing chip-like foam, electroconductive powder and liquid adhesive base with one another followed by injecting the resultant mixture with a curing agent under compression.

This radio wave absorber is obtained by mutually mixing (A) pref. 70-95 pts.wt. of chip-like resin foam (pref. flexible resin foam pref. 14-120kg/m3 in apparent density). (B) pref. 5-40 pts.wt. of electroconductive powder (e.g. carbon black) and (C) pref. 5-30 pts.wt. of a liquid adhesive base (pref. urethane prepolymer) followed by compressing the resultant mixture in a mold and then injecting, while maintaining the mixture generally in this state, the inside of the mold with (D) a gaseous or liquid curing agent reactive to the component C (pref. steam) to effect curing the component C. Thus, the objective radio wave absorber useful in e.g. radio wave darkrooms can be easily afforded.