Rutile TiO2 particles were partly dissolved into aqueous solutions of H2SO4, and the Ti4+ ions were reprecipitated by adding NH3 aq. Rutile-anatase coupled TiO2 particles were prepared by heating the solid recovered after centrifugation of the suspension. The content of anatase (C-A, wt%) could be controlled arbitrarily by changing the dissolved amount of rutile. The photocatalytic activity for the gas-phase oxidation of acetaldehyde was evaluated. The first-order rate constant, k, strongly depended on both C-A and heating temperature (T-c), increasing with an increase in T-c at T-c less than or equal to 800 degreesC. The sample with C-A = 0.5 wt% prepared at T-c = 800 degreesC exhibited a much higher level of activity (k = 0.94 h(-1) m(-2)) than those of pure rutile (k = 0.08 h(-1) m(-2)) and anatase (k = 0.34 h(-1) m(-2)). This remarkable enhancing effect was explained mainly in terms of photoinduced interfacial electron transfer from anatase to rutile. (C) 2003 Elsevier Inc. All rights reserved.