Surface characteristics and osteoblast cell functions were investigated for the nano-structured oxide layer on commercially pure titanium (CP-Ti) fabricated using microarc oxidation (MAO) and hydrothermal treatment (HT) methods. Ti-MAO-135HT, Ti-MAO-150HT, and Ti-MAO-175HT groups were fabricated by hydrothermally treating the MAO-treated specimens (Ti-MAO) in phosphorus-containing alkaline solution at temperatures of 135, 150, or 175 °C, respectively. After hydrothermal treatment, a nanosheet-shaped morphology, nano-needles and nanorods were observed on the porous surface of the Ti-MAO-135HT, Ti-MAO-150HT and Ti-MAO-175HT groups, respectively. The roughness was not significantly different for all groups. However the contact angle decreased dramatically as the hydrothermal temperature increased. The osteoblastic cell adhesion and viability of the Ti-MAO-150HT and Ti-MAO-175HT groups were significantly lower compared to those of the Ti-MAO group. This study showed that nano-topology formed on micro porous oxide layer was more important than hydrophilicity in its effect upon initial osteoblastic cell functions.