From the dried and fresh aerial parts of Senecio selloi Spreng, De Candolle (Asteraceae), the new triterpene ozonide 1 was isolated. Its structure was elucidated by NMR experiments, including inverse techniques HMQC and HMBC and by synthesis from the precursor 2 In contrast to natural peroxides, no antiplasmodial activity was detected for the ozonide 1.