Objectives : The purpose of this study is to isolate tyrosinase inhibitory material from Pinellia ternata and characterize its own structure and activity. Methods : Pinellia ternata (600g) was extracted with 95% methanol (1L) at $37^{circ}C$ for 4 days, with shaking at 250rpm. The extract was further solvent-fractionated with n-hexane, chloroform, ethylacetate and water. The active fraction was subjected to JAI recycling prep-HPLC JAIGEL GS-320 column. The structure was identified for the active peak with NMR and GC. Results : Tyrosinase was potently inhibited by 95% methanol extracts from Pinellia ternata. The $IC_{50}$ value of the extracts was estimated to be 0.05mg/ml. The extracts was divided into four solvent-fractions, and the most potent tyrosinase inhibition was found in ethylacetate layer. $IC_{50}$ value of ethylacetate fraction was 0.001mg/ml. This fraction was further purified with JAI Recycling Preparative HPLC (Model: LC 9104). The isolated compound showing inhibitory activity was characterized on its chemical structure by NMR and the compound was identified as 3,4-dihydroxybenzaldehyde. $IC_{50}$ was found to be 7.74 ${mu}M$ which is much lower than that of kojic acid $(66.5{mu}M)$. Conclusions : The data suggest that 3,4-dihydroxybenzaldehyde isolated and identified from Pinellia ternata is very strong inhibitor to melanin biosynthesis.