PURPOSE: To improve a radio wave absorbent in strength and flexibility so as to protect it against cracking and chipping at handling by a method wherein coupling agent is previously added to material powder possessed of radio wave absorbing power.

CONSTITUTION: Material powder polymethylpentene whose glass transition point is 20°C or below and at least one or more kinds of powder selected from Mn-Zn ferrite powder, magnetite powder, and graphite powder are uniformly mixed together to form material powder possessed of radio wave absorbing powder, and silane coupling agent is added to the material powder concerned. Polymethylpentene is a kind of hydrocarbon, so that it can not be expected to serve as a powerful coupling agent to combine directly and firmly with the radio wave absorbing material powder. A silane coupling agent is added to the radio wave absorbing material concerned, whereby polymethylpentene combines indirectly with the material concerned, in result a radio wave absorbent of this design can be improved in strength and flexibility.