Abstract: Siphonostegia chinensis Benth. as a traditional Chinese medicine "Liujinu"has been used for centuries in China, but up to date little has been reported about itschemistry. Now, four compounds have been isolated from the aerial parts of this genus. Onthe basis of spectroscopic analysis (UV, IR, MS,¹HNMR, ¹³CNMR and 2D-NMR)andchemical evidences, compound I was shown to be a new pyridinemonoterpene alkaloidwhich is a stereoisomer of the known compound cantleyine, and named isocantleyine. Itsstructure was determined as 5H- 2- pyridine- 4- carboxylic acid, 6, 7 - dihydro- 6-hydroxy-7-methyl- methyl ester. Compound Ⅲ was identified as the known com-pound loliolide. The other two ( Ⅱ and Ⅳ)are still under investigation. This paper deals mainly with the structure identification of compound I .