A new pyrrolizidine alkaloid, senecicannabine (4) which was isolated from Senecio cannabifolius was derived from seneciphylline (1) by oxidation with performic acid. The transformation of jacozine (6) to 4 was also carried out with performic acid, and the configuration of the epoxide ring of 6 was chemically determined to be 15S and 20S. © 1984, The Pharmaceutical Society of Japan. All rights reserved.