The purpose of the present work is to observe whether Tau protein Ser202/Thr205 is hyperphosphorylated in braintissues of diabetic mice and to study the effect of App17 peptide. Mouse diabetic model was produced with streptozotocin, andApp1 7 peptide as a treatment was injected subcutaneously into diabetic mice. Four weeks later, fixative was injected intravascu-larly into the mice, the brain was removed and crystat sections prepared. Immunohistochemical staining was done with AT-8. Inthe brains of diabetic mice positive AT-8 reacting neurons were numerous, darkly stained, and widely distributed in retrosplenialgranular cortex, hippocampus, thalamus et al. , while in normal mice and App17 peptide-treated diabetic mice positive cells werescarce and poorly stained. Tau protein is hyperphosphorylated at Scr202/Thr205 site and widely distributed in the brains of dia-betic mice, while App17 peptide can normalize the expression of AT-8 positive cells.