The water extracts of crude drugs of Taiwan Tang-Niao-Tung (T.N.T.) No. 2 and No. 3 were administered to normal and diabetic rats for investigating the antihyperglycemic effect of these two prescriptions. It was found that the blood glucose level in normal rats was temporarily increased after T.N.T. No. 2 and No. 3 administration; this may be caused by the starch content of the drugs component. In contrast, the diabetic rats have shown a significant decrease (P less than 0.01) of blood glucose in 2, 4, 6 hours after T.N.T. No. 2 and No. 3 have been given. The blood glucose percentage at 6 hours was 78.1% of T.N.T. No. 2 and 79.2% of T.N.T. No. 3 as compared to the original level. The hypoglycemic effect of T.N.T. No. 2 and No. 3 on alloxan-induced diabetic rats have suggested that action mechanism might not mediate through the release of insulin or positive feedback of glucose to insulin, neither acted on insulin receptor. It might be possible by the indirect promoting of enzyme activity. However, the pharmacological effect of some drugs could elucidate the hypoglycemic action of these prescriptions. Temporary promotion of blood glucose in normal rats will decline to normal level by 12 hours after T.N.T. No. 2 and No. 3 administration. The pharmacological effect of these herb prescriptions for diabetic rats is valuable for further study.