In the methanol extract from sliced tubers of konjak (Amorphophallus konjac, K. Koch), four polyphenolic substances were detected by two dimentional paper chromatography. These polyphenolic substances were fractienated into three fractions (basic, neutral and acidic fr.) by ion exchange chromatography on Amberlite CG 120 and CG 4B columns. From each fraction, catecholamine, flavanol type tannins and other polyphenol were found respectively by means of color reaction and UV light irradiation. The polyphenolic substance in basic fraction was purified by using Amberlite CG 50 column, and it was identified as dopamine (3, 4-dihydro xyphenylethylamine), since it gave 6, 7-hydroxy-1, 1-dimethyl-2, 3, 4-tetrahydroisoquinoline by the condensation reaction with acetone under neutral condition. Polyphenoloxidase (E. C. 1. 10. 3. 1.) prepared from the tubers of konjak showed high activity for catecholamines such as dopamine and DL-dopa. Therefore, it is likely that dopamine is a browning compound of konjak tubers. Other polyphenols detected also may take parts in the browning of tubers.