While short-term surface energy effects on cell adhesion are relatively well known, little is revealed as regards its later stage effects on cell behavior. We examined surface energy effects on osteoblastic cell growth and mineralization by using human fetal osteoblastic (hFOB) cells cultured on plasma-treated quartz (contact angle, theta=0 degrees) and octadecyltrichlorosilane (OTS)-treated quartz (theta=113 degrees). hFOB cells formed a homogeneous cell layer on plasma-treated quartz, while those cultured on OTS-treated quartz produced randomly distributed clump-like structures that were filled with cells (confirmed by confocal microscopy). Mineral deposition by hFOB cells was spatially homogeneous when cultured on hydrophilic surfaces. Furthermore, cells on hydrophilic surfaces exhibited increased mineralized area as well as enhanced mineral-to-matrix ratio (assessed by Fourier transform infrared spectroscopy), relative to cells on hydrophobic surfaces. Experiments using other types of osteoblast-like cells (MC3T3-E1, MG63, and SAOS-2) revealed more or less similar effects in spatial growth morphology. It was concluded that hydrophilic surfaces induce homogeneous spatial osteoblastic cell growth and mineral deposition and enhance the quantity (e.g., area) and quality (e.g., mineral-to-matrix ratio) of mineralization relative to hydrophobic surfaces. Our data suggest that surface energy effects on osteoblastic cell differentiation, especially mineralization, may be correlated with surface energy dependent changes in spatial cell growth.