Phytochemical investigation of Senecio obtusatus Wall. ex DC led to the isolation of a novel alkaloid, senobtusin (1). Compound 1 possesses an atypical amidine moiety, and the structure was determined on the basis of extensive NMR analysis and HR-ESI-MS technique. This is the first report of this class of natural products obtained from family Asteraceae, and the systematic importance was also discussed.