The hypoglycemic effects of Lagerstroemia speciosa L., known by the Tagalog name of banaba in the Phillipines, were studied using hereditary diabetic mice (Type II, KK-AY/Ta Jcl). The mice were fed a test diet containing 5% of the hot-water extract (HWE) from banaba leaves, 3% of the water eluent of the partial fraction unadsorbed onto HP-20 resin of HWE (HPWE), and 2% of the methanol eluent of the partial fraction adsorbed onto HP-20 resin of it (HPME) for a feeding period of 5 weeks. The elevation of blood plasma glucose level in non-insulin dependent diabetic mice fed the cellulose as control (CEL) diet were almost entirely suppressed by addition of either HWE or HPME in place of cellulose in the CEL diet. Water intakes were inclined to increase gradually in the group fed either CEL or HPWE, but lower in the mice fed either HWE or HPME than in the animals given either CEL or HPME. The level of serum insulin and the amount of urinary excreted glucose were also lowered in mice fed HWE. Plasma total cholesterol level was also lowered in mice fed the either HWE or HPME. It is suggested that HWE, especially HPME, obtained from banaba leaves have beneficial effects on control of the level of plasma glucose in non-insulin dependent diabetes mellitus.