Melanin is one of the most important factors affecting skin color, and inhibition of tyrosinase activity can effectively control melanin biosynthesis in the skin. This study was conducted to search and identify potential whitening ingredients from irradiated rutin using the mushroom tyrosinase inhibition method. The natural flavonoid glucoside rutin was easily degraded by gamma-irradiation into three new products: radioruinol (1), isoradiorutinol (2), and radiorutindiol (3). Structures of the new rutin derivatives, including absolute configurations, were elucidated based on spectroscopic interpretation (nuclear magnetic resonance, UV, circular dichroism, [α]D, and fast atom bombardment-mass spectrometry). The tyrosinase inhibitory activities of the newly formed rutin derivatives were evaluated. The new dihydroflavonol derivative radiorutindiol (3), containing two hydroxymethyl groups instead of olefin and ketone moieties, exhibited significantly improved inhibitory activity against tyrosinase with an IC50 value of 45.3±1.6 μM compared to the parent rutin. Gamma irradiation of rutin can be used to produce new compounds 1∼3 with enhanced tyrosinase inhibitory effects.