We synthesized pure rutile and anatase nanopowders using in-flight oxidation of titanium nitride powder in an r.f. thermal plasma reactor. The mechanism of the in-flight oxidation of TiN powder was elucidated, and the effects of oxygen and hydrogen input concentrations on phase composition and morphology were investigated. The characteristics of the synthesized powder were evaluated using X-ray diffraction, optical microscopy, scanning electron microscopy and Raman scattering spectroscopy. The phase composition depended mainly on the ambient oxygen concentration. At high oxygen concentrations, the anatase content increased to over 93%. Introducing hydrogen promoted the formation of oxygen-deficient rutile nanopowder, and pure rutile nanopowder averaging 50 nm in diameter was produced with excess hydrogen. The synthesized powder had good photocatalytic activity in the decomposition of aqueous methylene blue under visible light. (C) 2003 Elsevier B.V. All rights reserved.