A new alkaloid, acutudaurin, was isolated from cultured roots of Menispermum dauricum, a rich source of the chlorine-containing alkaloid acutumine and its dechlorinated analogue dechloroacutumine. The structure of acutudaurin was determined to be 2',3'-dihydro-5-hydroxy-4,6',7'-trimethoxy- 1'-methylspiro[3-cyclohexene-1,10'-[3a,7a]propano[1H]indole]-2,5'(4'H)-dione by spectroscopic methods.