The invention relates to application of oligomeric proantho cyanidins in preparing products for preventing, diagnosing, detecting, protecting, treating and studying vascular dementia and directly related diseases thereof, in particular to new application in medicament and health-care products. Experiments prove that oligomeric proantho cyanidins can improve the study memory ability of a heart andbrain ischemia-reperfusion mouse and a permanent bilateral common carotid arteries rat, inhibit lipid peroxidation in brains of the heart and brain ischemia-reperfusion mouse and the permanent bilateral common carotid arteries rat, and improve the superoxide dismutase enzyme activity of the heart and brain ischemia-reperfusion mouse and the permanent bilateral common carotid arteries rat. The oligomeric proantho cyanidins have strong action, clear effect, rich resource, simple preparation process, high yield, stable property and safe use, in particular one object with multiple functions and wide application range, and can play roles furthest. Disease rate of dementia rises gradually, after popularization, the application of oligomeric proantho cyanidins can generate significant social benefit and economic benefit in short time.