In the course of screening program for skin whitening compounds, flaniostatin (FST) was isolated from the leaves of Cudrania tricuspidata as a novel inhibitor of tyrosinase. The structure of FST was determined by ESI-MS and NMR spectroscopic analyses as a new isoflavone glycoside. The FST was exhibited a tyrosinase inhibitory effect in a dose-dependent manner. This effect was higher than that of arbutin at the same concentrations. These results indicated that FST isolated from C. tricuspidata may be a positive tool for skin-whitening agent research.