A chemical reaction of CrO3 with polymer molecules of poly vinyl alcohol (PVA) and sucrose in water is explored to synthesize CrO2 (D-4h(14) : P4(2)/mnm tetragonal crystal structure) of shape-controlled ferromagnetic particles. Under hot conditions, small species of Cr6+-PVA polymer chelates react in divided groups in micelles, resulting in a Cr4+-polymer complex, which retains in isolated groups of micelles dispersed in the water. When heating (after aging and drying), the polymer bums out at 300-400 degrees C in air, leaving behind a pure Cro(2) of prismatic or ellipsoidal shape. Average diameter varies in such particles from 50 to 300 nm depending on the final temperature. (c) 2005 Elsevier B.V. All rights reserved.