Stephania sutchuenensis H. S. Lo (Menispermaceae) is indigenous to the southwestern part of China, and its root is used in folkloric medicine to treat common cold, sore throat, and arthritic pain. We have previously reported on the occurrence of liriodenine, oxoanolobine, tetrandrhle, stephanonine, aknadinine, and i-nitroaknadinine in the root of this plant. In a continued study of the chemical composition of S. sutchuenensis, fresh roots were extracted with 95 % EtOH and separated into 5 % HC1-soluble and insoluble fractions. The acid-soluble part afforded three alkaloids: thalrugosine, pronuciferine, and sinococuline. Three lipids were also isolated from the acid-insoluble part: β-sitosterol, pentadecanoic acid ethyl ester, and palmitic acid ethyl ester. All compounds were purified by repeated chromatography, and identified by their spectroscopic characteristics ([α]D, UV, IR, 1H- and 13C-NMR, EI-MS). Sinococuline was reported to show in vivo antitumour activity against sarcoma 180 ascites and P388 lymphocytic leukaemia in mice. In a preliminary study, we have examined its in vitro cytotoxic effects using fibroblasts, tumour cell lines, and macrophages. Sinococuline exhibits a dose-dependent killing ability on all tumour cell lines tested, but not on the fibroblasts. It also interferes with the production of antitumour molecules such as tumour necrosis factor and reactive nitrogen intermediates by normal rat lung macrophages. Among these ingredients, sinococuline (1) is a rare morphinane alkaloid previously reported from only two plant sources, Cocculus trilobus and Stephania cepharantha. We have now obtained the 2-dimensional NMR data of this compound including 1H,1H-COSY, 1H, 13C-COSY, NOESY, and HMBC results. The HMBC experiment reveals the following long-range 1H-13C correlations: H-1 (C-3, C-1, C-13); H-2 (C-4, C-12); H-5 (C-9, C-13, C-14); H-7 (C-5, C-8, C-9); H-10 (C-8, C-9, C-1, C-12, C-14, C-16); H-11 (C-12, C-13); H-15 (C-13).