Rosmarinic acid and its methyl ester, isolated from the ethyl acetate soluble fraction of the methanolic extract of Salvia miltiorrhiza Bunge (Labiatae), were found to inhibit the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with the $IC_{50}$ values of 16.8 and $21.5;{mu}M$, respectively. It was comparable with kojic acid, a well-known tyrosinase inhibitor, with an $IC_{50}$ of $22.4;{mu}M$. The inhibitory kinetics analyzed by the Lineweaver-Burk plots, were found rosmarinic acid and its methyl ester to be competitive inhibitors with $K_i;of;2.4{ imes}10^{-5};and;1.5{ imes}10^{-5};M$, respectively.