Two new alkaloids, stemonamide (1) and isostemonamide (2), were isolated from the roots of a Chinese medicinal plant, Stemona japonica, collected from Zhejiang Province, People's Republic of China. Their structures were elucidated by spectral analyses and chemical conversion. The roots of Stemona japonica (Stemonaceae) and related Stemona plants are used as insecticides and cough-relief agents. In our systematic investigation of alkaloids of Chinese Stemona plants, we have found almost all of the alkaloids present to have the same 4-aza-azulene basic ring skeleton. These structures can be separated into seven groups according to the sites of connection between the basic ring and the side-chain. In a previous publication (1), we have reported the presence of protostemonine-type alkaloids in this plant. The present study reports five maistemonine-type alkaloids in which maistemonine (5) could be regarded as a typical compound. According to a literature report, two alkaloids of this type, stemonamine and isostemonamine, have been isolated from the roots of S. japonica by Iizuka et al. (2). The structure of stemonamine (3) was determined by X-ray analysis and the structure of isostemonamine was also proposed as (4) (2). We have reported previously the structure of maistemonine and oxymaistemonine (3). On the basis of spectral comparison and chemical conversion, two new alkaloids, stemonamide (1) and isostemonamide (2), along with the known stemonamine (3), isostemonamine (4) and maistemonine (5) have been isolated and identified by spectral analysis and chemical correlation. The structures of maistemonine (5) and the related oxymaistemonine (6) have been corrected.