The complex formation of uranium (VI) with 2, 2', 3, 4-tetrahydroxy-3'-sulpho-5'-chlorazobenzol (R) was studied. There is formed a homogenous complex with 1:2 molar ratio of components, maximum light absorption of complex is observed at 490 nm, molar coefficient of absorption is 6250. It was produced a new sorbent. There was a static sorption capacity on K+ ions and there were determined the constants of ionization of ionogenic groups by potentiometric titration. It was investigated the conditions of concentration of uranium with that sorbent. The degree of extraction of U (VI) ions at optimal conditions is more than 95%. Limits of detection (3, n=20) are 14.2 ng/ml. It was worked out a technique of photometric determination of U (VI) in sea water.