Functional fiber containing iso-thiourea group was prepared by reactive chloromethylated poly(vinyl acetate)-gradt-polystyrene-divinylbenzene (PVA-g-PS-DVB) being reacted with thiourea. The functional group content of the fiber was 2.90 mmol/g. The chloromethylated PVA-g-PS-DVB reacted with sulfur atoms in the thiourea molecules; this made the fiber containing iso-thiourea group. The results of static adsorption experiments showed that the adsorption amount of the fiber toward Au(III) reached a maximum amount, 1000 mg/g, at pH 1.5. It reduced the adsorbed Au(III) into Au(0), and the maximum reduction percentage was 90% at pH 2.0. The amount of Au(III) adsorbed by the fiber increased with increasing solution temperature but decreased with the increasing ionic strength of the solution. It was proven by electron spectroscopy for chemical analysis that some of the sulfur atoms in the fiber were oxidized into sulfone groups or sulfate ions.