Abstract: The pharmaceutical composition contains an effective amount of a tungsten (VI) compound, preferably a tungstate or a isopolytungstate, and more preferably sodium tungstate. In the method of lowering blood sugar in a human suffering from type I or type II diabetes mellitus, an effective amount of the composition is administered orally. Compared with the known vanadium compositions, the invention has the advantage of providing a similar high sugar-lowering activity but with a much lower oral toxicity at effective doses, both short- and long-term. Compared with insulin, the invention does not present the adverse effect of inducing hypoglycemia when administered in excess.