Aconitine, a major Aconitum alkaloid, is well known for its high toxicity that induces severe arrhythmias leading to death. However, aconitine has been used as one of the most popular compounds in Shino-Japanese traditional herbal medicine. Little has been reported concerned with the long-term effects of aconitine. Therefore, the authors investigated the physiological effects of chronic administrations of aconitine by determining the changes in body weight and rectal temperature of mice, compared with the concentrations of aconitine and its metabolites (benzoylaconine and aconine) in the liver and kidneys. The concentration ratio of aconitine to the total Aconitum alkaloids (from day 0 to 22; 90 min after the last administration) gradually decreased, whereas its metabolites increased until day 22. The body weight gain in aconitine-administered group was less than that of the control group until day 22. Transient rectal hypothermia occurred within 30 min after the last administration of aconitine. Then the rectal temperature gradually increased to normal level in respect to time. This study might reveal the possibilities that the drug metabolism of aconitine increased and the toxicity of aconitine decreased due to long-term administrations of aconitine.