Surface silanol group (SiOH) has been analyzed using Static SIMS. In general, adsorption properties or surface reactivity of silicate glasses are influenced by the surface silanol group, though determination has been difficult up to now. In this study, detection of 45SiOH+ cluster fragment ion has been successfully applied to estimate the surface silanol group in silicate glasses. The absolute determination was achieved by using a calibration curve obtained from measurement of a quartz glass as a reference sample. The surface silanol concentration of the quartz glass was determined by analysis of O1s photoelectron line provided by XPS. The developed technique was applied to analyze the soda-lime-silica glass and silica films. On the basis of this analysis, the role of the surface silanol group has been discussed in terms of surface adsorption.