Two new morphinane alkaloids named cephamonine (1) and cephamuline (2) were isolated from the tuber of Stephania cepharantha HAYATA (Menispermaceae), cultivated in Japan, along with eleven known alkaloids. By comparison of spectroscopic data with those of sinomenine (3), the structures of 1 and 2 were elucidated to be the 8-methoxy derivative of 3 and its C-14 stereoisomer, respectively.