Apatite was precipitated on the surface of titanium dioxide (TiO2) powder by a biomimetic process. The precipitation was accomplished by immersing TiO2 powder in simulated body fluid (SBF) for 1, 3, 6, 12 and 24 h. Photocatalytic activity of the apatite-precipitated TiO2 (HAp-TiO2) powders was investigated to assess the decomposition of methylene blue (MB) in aqueous solution and the removal of acetaldehyde gas under UV irradiation. Hydroxyapatite precipitation enhanced the photocatalytic activity of the TiO2 powder. The time required for the complete degradation of MB decreased from 3.5 to 2 h with the immersion of TiO2 powders in SBF for 3 h. In terms of acetaldehyde gas decomposition, less than 1 h was sufficient to achieve complete removal for HAp-TiO2 powder but at least 2 h were required for the bare TiO2 powder. HAp-TiO2 powders could therefore be a promising candidate photocatalyst for environmental purification.