From flower buds of Aconitum carmichaeli Debx., a new alkaloid, 8- O-cinnamoylneoline, was isolated. The structure of the new alkaloid was determined by spectral analysis, and the alkaloid was examined for its toxic and analgesic activities. Its LD50 value was 11.89 mg/kg (s.c.) in mice: the toxicity was 1/30 times that of mesaconitine and 20 times that of benzoylmesaconine. Its ED50 value was 0.86 mg/kg (s.c.) in mice using the tail pressure method: its analgesic effect was 1/40 times that of mesaconitine and 45 times that of benzoylmesaconine. Its safety margin (= LD50/ED50) was higher than that of benzoylmesaconine but lower than that of mesaconitine.