Phosphoric cation exchange resins, of different diametem from 0.16 to 0.76 mm., with venous dogree of cross-licking, have been prepared by the copolymerization of styrenedivinylbenzeue, followed by the reaction with phosphorus trichloride in the presence of aluminum chloride, and finally by the oxidation with nitric acid. The capacity, swelling, and moisture content vary inversely with increase of the degree of croay-linking and with the particle size of the resin. From the results of phospliorus analyses and capacity determination, it is thown that each benzene ring contains approximately 0.76-0.86 atom of phos- photos which exists mainly as phosphoric acid. The potentiometric titration curve proves that the resins are dibasic acids.