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Visible-light photocatalytically active titanium oxide (TiO₂) nano-powder was synthesized by a flat-flame chemical vapor condensation method. The formation of TiO₂ consisting of different ratios of anatase and rutile phases was controlled by two parameters: the acetylene flow rate (C₂H₂, 600 sccm and 800 sccm) and the acetylene/oxygen flow ratio (C₂H₂/O₂, 1:3, 1:4, 1:5, and 1:6). The location of the photonic center was identified for visible-light absorption, which is in the anatase grains. The photonic center on the surface of anatase grains happens to be the nucleation site for rutile in an oxygen-deficient environment. The visible-light absorption could be attributed to the formation of defect levels related to the photonic center within the band gap of anatase. The major role of the mixed-phase structure of TiO₂ in the enhancement of visible-light photocatalytic activity is in the enhancement of carrier separation and not of light harvest, for the powder produced in this study.