Abstract: The authors studied the oxidation of macroporous chloromethylated copolymer of styrene-divinylbenzene with nitric acid to macroporous copolymer of vinylbenzoic acid-divinylbenzene (CVBD); thus the weakly cation exchange resins with capacities of 5.0-5.7meq/g(H)were obtained. The effects of the reaction conditions such as the concentration of nitric acid, the temperature and time, were investigated. The reactions of the chloromethylated styrene-divinylbenzene copolymer with dilute nitric acid in the presence of potassium nitrate and surfactants were also investigated. The infrared spectra of the resins proved the composition of the products;it also indicated that the oxidation of the chloromethylated copolymer of styrene-divinylbenzene with concentrated nitric acid first formed an ester as intermediate, i. e. benzyl nitrate, and then to CVBD. The side reaction, i. e. the cleavage of the main chain of the copolymer, was discussed and the degree of decrosslinking of the resins in the reaction was estimated by means of a plot of the swelling against the weight capacity of the resin.