A silane coupling agent, CF3(CF2)(9)CH2CH2Si(NCO)(3), prepared by hydrosilylation of trichlorosilane with CF3(CF2)(9) CH=CH2 in the presence of hydrogen hexachloroplatinate(IV), followed by reaction with silver cyanate, was used for glass and bovine tooth surface modification. In ESCA of the modified glass surfaces, nitrogen atoms in the silane coupling agent bound to the surfaces were detected only at contamination levels. This ESCA revealed that neither urethane bonds nor NCO groups were present on the modified glass surfaces. Clear AFM images of the modified glass surfaces were also obtained. Though the contact angles of water on the modified glass surfaces were independent of the modification time (20 min or 4 h), the AFM images obtained show that the original glass-surface patterns of unevenness remained on the surfaces in the case of the short modification time (20 min), whereas they disappeared from the surfaces in the case of the long modification time (4 h). In the latter case (4 h), the silane coupling agent reacted sufficiently over the entire glass surface, and no region of unmodified glass surface was detected. The surfaces of bovine tooth specimens were modified with this silane coupling agent by spreading of the agent on the surfaces with a small brush followed by brief drying with a hair drier. The amounts of plaque adhering to the modified and unmodified bovine tooth surfaces after wearing of the specimens in a human oral cavity for five days were compared. The amounts of plaque adhering to these specimens in in vitro tests as determined from SEM images were also compared. It is expected that this silane coupling agent will be useful as a plaque-controlling surface modifier for enhancement of oral health.