A new diterpenoid alkaloid cossonidine (1) has been isolated from Delphinium cossonianum and Delphinium cadiopetalum. The structure of cossonidine was determined by spectroscopic methods, including 1H COSY, HMQC, HMBC, and ROESY NMR experiments, and chemical transformations. The NMR data of kobusine (5) and sanyonamine (6) are also presented.