Blood glucose lowering effects of water extracts from four species of Commelinaceae(Commelina communis, Streptolirion volubile, Tradescantia reflexa, Aneliema keisak) were determined on alloxan-induced hyperglycemic rats. In all the experimental groups, the blood glucose level decreased after loading carbohydrates. The blood glucose level in a group treated with C. communis extract decreased significantly as compared with the normal group. After loading maltose and sucrose separately in different groups, the blood glucose level decreased in the groups treated with the extracts of C. communis and S. volubile, and remained approximately unchanged with the extracts of T. reflexa and A. keisak as compared with the control groups.