The major and minor constituents of silica scale samples collected from different geothermal power stations in Japan were determined by atomic absorption spectro- photometry and neutron activation analysis. These samples are all low in elements characteristic to hydrothermal ore deposits, such as Au, Ag, As and Sb. Some samples are found to be enriched in Rb and Cs, the amount of which is apparently related to Rb and Cs concentrations in geothermal waters^ and also to the Al content of silica scales. The distribution ratio of alkaline metals between silica scale and geothermal waters decreases in the order of Cs, Rb, K, Na and Li.