In this work, 12 μm titanium oxide (TiO2) nanotube arrays were formed by the anodization of titanium (Ti) foil in ethylene glycol containing 1 wt% water and 5 wt% fluoride for 60 min at 60 V. After annealing at 400 °C in argon for 4 hr, TiO2 nanotube arrays were immersed in 0.02 M phosphoric acid (H3PO4) to incorporate phosphorus (P) into TiO2 nanotube arrays. Results from x-ray photoelectron spectra revealed that the P-incorporated TiO2 nanotubes contained Ti, oxygen (O), P and carbon (C) after wet impregnation process. The photocatalytic activity of the nanotube arrays immersed in H3PO4 at various impregnation times was evaluated by monitoring the degradation of methyl orange. Results indicate that the nanotube immersed in H3PO4 for 90 minutes with an average diameter of 100 nm and an optimal tube length of 12 μm with a thin tube wall (20 nm) is the optimum structure required to achieve high photocatalytic reaction. The incorporated C and P into TiO2 nanotube arrays is believed to provide a shallow trap for photo-generated e- and h+, inhibiting the recombination and extending the lifetime of the charge carriers. Thus, this sample resulted in high degradation of methyl orange as compared with other samples. In addition, the existence of C, P, and high degree of anatase crystallinity, smooth wall and absence of fluoride enhanced the photocatalytic activity of the sample.