The titanium dioxide (TiO(2)) nanotube surface enables significantly accelerated osteoblast adhesion and exhibits strong bonding with bone. We prepared various sizes (30-100 nm diameter) of titanium dioxide (TiO(2)) nanotubes on titanium substrates by anodization and investigated the osteoblast cellular behavior in response to these different nanotube sizes. The unique and striking result of this study is that a change in osteoblast behavior is obtained in a relatively narrow range of nanotube dimensions, with small diameter ( approximately 30 nm) nanotubes promoting the highest degree of osteoblast adhesion, while larger diameter (70-100 nm) nanotubes elicit a lower population of cells with extremely elongated cellular morphology and much higher alkaline phosphatase levels. Increased elongation of nuclei was also observed with larger diameter nanotubes. By controlling the nanotopography, large diameter nanotubes, in the approximately 100 nm regime, induced extremely elongated cellular shapes, with an aspect ratio of 11:1, which resulted in substantially enhanced up-regulation of alkaline phosphatase activity, suggesting greater bone-forming ability than nanotubes with smaller diameters. Such nanotube structures, already being a strongly osseointegrating implant material, offer encouraging implications for the development and optimization of novel orthopedics-related treatments with precise control toward desired cell and bone growth behavior.