PURPOSE: To obtain a cheap arsenic capturing material easy to handle and showing a superior adsorbing property to arsenic contained in liquid by reducing a keratin- contg. substance.

CONSTITUTION: A keratin-contg. substance such as waste fibers formed from a wool spinning process, etc. or feathers discharged from the chicken industry is expanded and reduxed at pH 4W11 with a reducing agent dissolved in a liquid medium such as water or alcohols. Thus, the disulfide bonds of the keratin is cleaved to thiol groups. The reducing agent includes thiol derivatives such as thioglycolic acid and phosphorus-contg. cpds. such as triphenyl phosphine. The thiol groups of the reduced keratin-cntg. substance may be oxidized or cross linked to obtain granules of large surface area. The resulting arsenic capturing material is in the form of fibers, granules, a membrane, etc., so it is easy to handle.