The aim of this study was to investigate the behavior of rat periodontal ligament (PDL) cells cultured on fibroblast growth factor-2 (FGF-2)-immobilized titanium surfaces treated by oxygen (O2) plasma. We used cell disks (15 mm in diameter), and 35-mm culture dishes sputter-coated with titanium. These were treated with oxygen plasma and dipped in FGF-2 solution. Immobilized FGF-2 was visualized with a confocal laser-scanning microscope, and its weight was calculated to be approximately 22.6 ng/cm(2) using a quartz crystal microbalance-dissipation apparatus. The PDL cells were obtained from rat incisors. Cells from fourth subculture were seeded onto the FGF-2-immobilized titanium surface. Proliferation ratio, alkaline phosphatase (ALP) activity, and expressions of type I collagen and vascular endothelial growth factor (VEGF) mRNAs were evaluated. Proliferation ratio and expressions of type I collagen and VEGF mRNAs were significantly higher, whereas ALP activity was significantly lower in FGF-2-immobilized cells than in control group (p < 0.05). These findings suggest that oxygen plasma modification can immobilize FGF-2 onto a titanium surface. Immobilized FGF-2, although inferior to culture medium with FGF-2, influenced the proliferation of PDL cells and might have promoted collagen and vascular synthesis.