Abstract:Abstract Three C18-diterpenoid alkaloids were isolated from Aconitum forre-stii Stapf collected in Lijiang area, Yunnan province, at the altitute of 3200 m, two known alkaloids, aconosine( 1 ), dolaconitine( 2 ), and one new alkaloid, lico-nosine A ( 3 ) , whose structures were determined based on spectroscopic evidence.It is interesting to note that liconosine A (3) , whose structure feature is dealkyled and with N=C double bond, appears to be unique in the C18-diterpenoid alkaloids. More than interesting is that the chemical components of this plant is different according to its growing altitute. The once studied Aconitum forrestii Stapf collected in Lijiang area, Yunnan province, at the altitute of 3500 m, con-tained thirteen C19-diterpenoid alkaloids, which indicates that difference in plant growing altitute leads to different chemical types. Since C19-diterpenoid alkaloids are more evolved than G19-type, the above result will possibly be significant for chemical ecology.