Nitrogen-doped titania was prepared by planetary ball milling of P-25 titania with ammonium carbonate. The effects of reaction conditions on the phase composition, particle size, optical property, and photocatalytic activity were investigated in detail. The high mechanical energy accelerated the phase transformation of anatase to brookite and rutile. The prepared powders possessed two absorption edges around 405 and 550 nm, and showed excellent photocatalytic ability for nitrogen monoxide oxidation under visible light irradiation. Under the irradiation of visible light (wavelength >510 nm), nearly 28% of nitrogen monoxide could be continuously removed by the nitrogen-doped titania that was prepared by planetary milling of P-25 titania-10wt.% ammonium carbonate mixture at 700 rpm for such short time as 15 min. (C) 2004 Elsevier B.V. All rights reserved.