The effects of different concentrations of the crude tea extracts ofLagerstroemia speciosa, on the alpha-amylase activity were determined. Since Banaba or L. speciosa lowers blood sugar, researches were directed towards the effects of the plant to ailments such as obesity, hyperglycemia, and diabetes. Rice is the staple food in the Philippines and is primarily made up of starch, a homopolysaccharide made up of glucose units. In the small intestine, pancreatic amylase then hydrolyzes the partially digested starch into smaller oligosaccharides which is then excreted into the lumen, and hydrolyzed into glucose. The enzyme alpha-amylase or alpha-1, 4 – glucan – 4 – glucanohydrolasescatalyzes the hydrolysis of alpha – 1, 4 – D- glycosidic linkages. Alpha-amylase inhibitors have been shown to have an effect in starch digestion and amount of glucose in the bloodstream. The effect of various concentration of crude extracts of L. speciosa on the kinetics of alpha-amylase were determined using the Bernfeld Assay. Starch was used as the substrate whereas porcine pancreatin was the source of alpha-amylase. Various amounts of crude water extracts of Banaba leaves were used. The Michaelis – Menten constant (Km) and the maximum velocity (Vmax) were measured. Results show that the alpha-amylase activity with the crude extract at a concentration as low as 0.50-mL demonstrated a significant reduction of the Km and Vmax values. With an increase in the amount of the crude water extracts, there was a slight decrease on the kinetics signifying a noncompetitive or an uncompetitive inhibition. The results of the study may provide a basis to design a treatment for diabetes or to lower the blood glucose level of diabetic patients.