Arbutin and deoxy arbutin may release hydroquinone under some conditions. We therefore investigated the photostability of arbutin and deoxy arbutin in an aqueous solution. The results revealed arbutin and deoxy arbutin to be photolabile in an aqueous solution. Deoxy arbutin was less stable than arbutin when exposed to UV radiation. The hydroquinone concentration was also increased during the radiation period in both solutions. Benzophenone-4 could clearly improve the photostability of arbutin during the period of UV radiation, but only slightly enhance the photostability of deoxy arbutin.