Chemical constituents in the alkaloidal fraction of the bark of Formosan X. nitidum (ROXB.) D.C. (F. nitida ROXB.) (Japanese name : Teriha-Zansho), Rutaceae, which was collected in the area of Ping-Tung Hsien, were examined. Twelve alkaloids [nitidine (1), oxynitidine (2), 6-methoxy-5, 7-dihydrochelerythrine (4), oxychelerythrine (6), des-N-methyl-chelerythrine (7), chelerythrine (14), arnottianamide (24), liriodenine (25), bocconoline (26), decarine (27), integriamide (28), and isoarnottianamide (13)] and three lignans [l-asarinin (20), l-sesamin (21), and l-syringaresinol (29)], a coumarin, aesculetin dimethyl ether (22), together with β-sitosterol (23) were isolated. Other than the above seventeen known compounds a new phenolic benzo [c] phenanthridone alkaloid designated as oxyterihanine (30a) was also isolated as a minor component. While the past three groups reported that nitidine (1) was a sole quaternary benzo-[c] phenanthridine alkaloid in the same plants collected in the areas of Hong-Kong and of China mainland (Gauanx and Gauantung), in our case, chelerythrine (14) was isolated as a major component. Nitidine (1) was isolated from the plant collected at March as a second component, but chelecythrine (14) was essentially a sole benzo [c] phenanthridine alkaloid in the case of the plant collected at July and at September. The seasonal variation of the contents of the quaternary benzo [c] phenanthridine alkaloids is discussed.