Simvastatin acid (SVA) has been reported to stimulate bone formation with increased expression of BMP-2. Therefore, immobilization of SVA onto dental implants is expected to promote osteogenesis at the bone tissue/implant interface. The aim of this study was to evaluate the immobilization behavior of SVA onto titanium (Ti), O 2 -plasma treated titanium (Ti + O2), thin-film coatings of hexamethyldisiloxane (HMDSO), and O 2 -plasma treated HMDSO (HMDSO + O2) by using the quartz crystal microbalance-dissipation (QCM-D) technique. HMDSO surfaces were activated by the introduction of an OH group and/or O 2 -functional groups by O 2 -plasma treatment. In contrast, titanium surfaces showed no appreciable compositional changes by O 2 -plasma treatment. The QCM-D technique enabled evaluation even at the adsorption behavior of a substance with a low molecular weight such as simvastatin. The largest amount of SVA was adsorbed on O 2 -plasma treated HMDSO surfaces compared to untreated titanium, HMDSO-coated titanium, and O 2 -plasma treated titanium. These findings suggested that the adsorption of SVA was enhanced on more hydrophilic surfaces concomitant with the presence of an OH group and/or O 2 -functional group resulting from the O 2 -plasma treatment, and that an organic film of HMDSO followed by O 2 -plasma treatment is a promising method for the adsorption of SVA in dental implant systems.Simvastatin, one of the liposoluble statins [inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase], has been widely used for lowering cholesterol levels. Recently, simvastatin was reported to stimulate bone formation both in vitro and in vivo in animal models of osteoporosis (10,25). This phenomenon was associated with increased expression of the bone morphogenetic protein-2 (BMP-2) gene in bone cells. Therefore, immobilization of simvastatin onto titanium implants is expected to promote osteogenesis in the bone tissue surrounding the implants through its topical application. Furthermore, one distinct advantage of simvastatin for local stimulation of bone formation is its low manufacturing cost compared to the direct administration of recombinant proteins such as BMPs. There is also a reduced possibility of eliciting antibody responses.Plasma-surface modification including plasma polymerization and plasma surface treatment is an effective and economical surface treatment technique for many materials. The technique is of growing interest in biomedical engineering because it can control the physicochemical properties of biomaterials