A new minor diterpenoid alkaloid, caeruline, was isolated from Delphinium caeruleum Jacq. ex Camb. Its structure was elucidated as 1 on the basis of spectral evidence. Along with this new compound, three known diterpenoid alkaloids were also isolated from this plant and identified as tatsiensine, delcosine, and lycoctonine which had not been found in this herb previously.