An inhibitor of human tyrosinase activity in rum distillate wastewater was isolated and identified as (S)-(+)-imperanene (1). (S)-(+)-Imperanene significantly inhibited tyrosinase isolated from HMV-II cells (IC(50) 1.85 mM). Inhibition kinetics studies revealed that imperanene is a competitive inhibitor of tyrosinase when L-3,4-dihydroxyphenylalanine is used as the substrate. The inhibitory activities of 1, O-beta-D-glucopyranosyl imperanene (2) and O-beta-D-glucopyranosyl-3-methoxyl imperanene (3) were 1>2>3.