High crosslinked copolymers based on poly(ethylstyrene-co-divinylbenzene), bead shaped, have chlorinated, resulting in adsorbents with a high content of chlorine (45.0% Cl). The chlorination process of the copolymer beads (0.40-0.80 mm in diameter) was carried out in 1,2-dichloroethane in the presence of a Friedel-Crafts catalyst (AlCl3, FeCl3), at 5-40 degrees C, yielding yellow beads without any cracks and good mechanical strength. The chlorination degree of the samples is high because each vinyl aromatic unit contains 1.8-2.2 chlorine atoms. The chlorinated copolymer samples were used to retain Cephalosporine C from standard solutions comparatively with commercial adsorbents (Amberlite XAD-4 Rohm, Haas Co.; SP-206/7, Mitsubishi Kasai Corp., Japan).