Diabetes Mellitus is a chronic disorder of carbohydrate metabolism whose prevalence is rising globally. The hypoglycemic property of raw Allium cepa has been established by several authors, and this study, was carried out to investigate the effect of heat on the hypoglycemic property of Allium cepa. This is against the backdrop that Allium cepa is mostly consumed boiled in Africa and several parts of the World. 40 Wistar rats were used for the study and diabetes was induced in 35 of them using single intraperitoneal dose of 40mgkg -1 of alloxan monohydrate. There were eight groups (n= 5). Group one and two served as the control groups, group three is insulin and group four is metformin. Group five to eight were treatment groups. Result showed the following reduction at 400 mgkg -1 (raw-57.2%; boiled-41.3%). At 600 mgkg ) show plasma glucose reduction of (52.7%) and (12.3%) respectively when compared with the control. Result shows that heat reduces hypoglycemic property of onions.