Processed Aconiti tuber (Aconitum carmichaeli) has been known as a potent analgesic herbal medicine in Japan and China. TJ-3021 [Tsumura Kampo Medicine Shuchi-Bushi Powder for Ethical Dispensing] is a herbal medicine produced from Aconiti tuber by autoclaving to decrease its toxicity. In the present investigation the antinociceptive mechanism of TJ-3021 in rats was studied. It was observed that under repeated cold stress (RCS), the administration of distilled water (p.o.) significantly increased the contents of norepinephrine (NE) in the cerebral cortex compared with rats without RCS. However, the administration of TJ-3021 decreased the NE contents in the cerebral cortex in rats with RCS. On the other hand, the administration of water in rats with RCS significantly decreased the contents of serotonin (5-HT) in the medulla. The administration of TJ-3021, on the other hand, increased 5-HT contents in the medulla in rats with RCS. It might be possible that the antinociceptic mechanism of the action of TJ-3021 could be attributed to the improvement of dysfunction of descending nociceptive 5-HT system.