The prevalence of Diabetes mellitus, a multiorgan system metabolic disease is on the increase even in developing countries like Nigeria. This study therefore investigated the protective effects of stem bark extract of Garcinia kola on the histology of pancreas of alloxan induced diabetic whistar rats using histological and histochemical techniques. The animals used in this study were divided into 6 groups viz: Control group, Diabetic control group, Garcinia kola stem bark only group, Diabetic+Glibenclamide group, Diabetic+low Dose Garcinia kola group and Diabetic+High Dose Garcinia kola group. The duration of study was 56 days. Studies on the rats on days 7 and 14 were regarded as short and medium term effect study. Day 21 study was taken as long term effect study while day 56 study was for reversibility study as treatment had been discontinued. On day 7, 14, 21 and 56, 3 rats from each group were sacrificed under chloroform anaesthesia and pancreas harvested for histological assay. The data obtained were analysed using GraphPad Prism® software version 6.01 to determine the mean and standard error of mean, changes in body weight, insulin and glucose levels were represented in percentages while one-way ANOVA at 95% confidence interval (p<0.05) was used to show the level of significance. Results revealed that the histology of the pancreas was grossly distorted in the diabetic control group animals whereas histology of the glibenclamide and Garcinia kola stem bark treated groups showed grossly repaired pancreas. These results demonstrate a protective effect of the hydro-methanolic extract of G.kola stem bark on organ damage in Diabetic mellitus.