The structure of tuguaconitine, MP $196{sim}198^{circ}C$, a new diterpene alkaloid isolated from the roots of Aconitum sibiricum P., was studied. Its empirical formula is $C_{23}H_{35}NO_7$ and spectroscopic evidence shows that the base contains three methoxyl, three hydroxyl and one N-ethyl groups. The acute toxicities of most of Aconitum species were strong and the acute toxicity of the alkaloid fraction of A. sibiricum was decreased by Glycyrrhizae, black bean or Zingiberis extract.