Diabetes is a growing health problem in the Philippines, which is characterized by hyperglycemia resulting from defects in pancreatic insulin secretion. The leaves of Lagerstroemia speciosa (L.) Pers., a Southeast Asian tree commonly known as banaba, have been traditionally consumed by Filipinos as medication. Its leaves are known to contain an active compound called corosolic acid, to which its glucose-lowering activity is attributed. Thus, the study was therefore intended to investigate the effect of ethanolic leaf extract of banaba on blood glucose and insulin. Likewise, it was designed to assess its protective activity by measuring insulin secretion of pancreatic β cells at different doses. Diabetes was induced intraperitoneally with alloxan (40 mg/kg) and banaba crude leaf extract was given orally once a day for 10 days. Results of the present study indicated significant decrease (p<0.05) in glucose levels and increase in insulin levels after treatment. On the other hand, protective activity to pancreas was evaluated by giving three doses of banaba crude leaf extract prior to treatment with alloxan, specifically 500, 1000 and 2000 mg/kg being Groups II, III, and IV, respectively with Group I being the normal control group. Significant rise in insulin levels was observed in Group II (1000 mg/kg) with a greater increase in Group IV (2000 mg/kg). Multiple comparisons by post-hoc analysis were conducted using Tukey method which revealed significant differences among the normal group, Group III and Group IV. All results were supplemented by histopathological analysis which indicated that both Group III and Group IV have favorable effects, though the latter showed a closer tonormal structure of pancreatic islet cells. Based on these findings, Lagerstroemia speciosa (L.) Pers. crude leaf extract exhibited hypoglycemic and The Steth, Vol. 8, 2014 2 ISSN: 2094-5906 protective activity at 1000 mg/kg and 2000 mg/kg concentrations, respectively.