In order to elucidate whitening mechanisms of arbutin (hydroquinone-O-beta-D-glucopyranoside), its effects on mushroom tyrosinase were analyzed by spectrophotometric, polarographic, and HPLC experiments. It was found that as soon as catalytic amounts of L-DOPA become available as a cofactor, arbutin acts as a monophenol substrate. A significant enzymatic product was identified as 3,4-dihydroxyphenyl-O-beta-D-glucopyranoside by NMR and MS experiments.