Background: Diabetes Mellitus (DM) is a worldwide common disease and it is considered a serious public health disorder .The reproductive function is highly sensitive to changes in metabolic status, with defective reproductive capacity. Aim of Work: To demonstrate the histological changes in the prostate of rats with STZ induced diabetes type and to examine to what extent insulin could reverse such changes. Materials and methods: Twenty six male albino rats were divided into three groups. Group I: control; Group II: Diabetic was exposed to induction of diabetes by a single intraperitoneal injection of Streptozotocin(STZ) 60 mg/kg in 0.1 M citrate buffer; Group III: Diabetic then received insulin (3IU/day S.C( (for 4 weeks). The rats of each group were sacrificed after 4 weeks. The prostates were processed for electron microscopic sections and other sections stained with H&E, Masson's trichrome, immunohistochemical staining of α smooth muscle actin, Vimentin and PCNA and statistical analysis were applied. Results: Diabetes resulted in deterioration of normal structure of the prostatic acini and some prostatic acini showed cell proliferation with increase Masson's trichrome staining  and increase immunoreactivity for α smooth muscle actin, Vimentin  and PCNA. Electron microscopic examination reavealed dilatation of the cisternae of the Golgi complex, endoplasmic reticulum, and some epithelial cells showed proliferation and irregular contour of their nuclei. Insulin administration mostly reversed these changes. Conclusion: insulin administration greatly improved the histological architecture of the prostate gland.