Copolymers of 4-vinylpyridine/8% divinylbenzene were prepared and chemically modified by monochloracetic and acrylic acids. Investigations of the iron(III) states in the modified copolymer phase were performed using Mossbauer and IR spectroscopies. It is shown that the sorption of iron(III) ions from an Fe(NO3)(3) solution is achieved by complexation of the cations with the carboxylic groups of the copolymer. The sorption of iron(III) ions from Fe-2(SO4)(3) solutions is achieved by both complexation of the cations with carboxylic groups and the formation of the jarosite-type compound R4N[Fe-3(SO4)(2)(OH)(6)]. On boiling in an aqueous medium the jarosite-type compound is transformed into highly dispersed particles of beta-FeOOH. During completion of three "sorption-boiling in aqueous medium" cycles a proportion of the beta-FeOOH particles becomes massive and magnetically ordered, but another portion remains in the highly dispersed superparamagnetic state distributed in the narrow pores of the modified copolymer.