Individual rainfall events are recorded as thin clay bands in annually laminated, freshwater-carbonate tufa. Runoff from rainfall events entrains clay that then adheres to the tufa surface. A specimen collected from southwest Japan exhibits >100 clay bands formed during a 15 yr period from 1988 to 2002. The chronology of the clay bands was determined by using the temperature-dependent cycle of oxygen isotope ratios in the carbonate, and the clay content was quantified by electron-probe microanalysis Si X-ray strength. The obtained Si X-ray strength curve and actual rainfall record follow a nearly identical pattern. The clay content of each band correlates with rainfall amount. Rainfall of >50 mm/week produced sufficient amounts of suspended cave clay to produce clay bands in the tufa. Because the clay bands survive postdepositional alteration, this new method can be applied to ancient tufa deposits and has great potential as a high-resolution rainfall record for use in climate studies.