Abstract: AIM　To study the effects of hydrocortisone（HC）on the learning and memory function and it′s mechanism related to the oxygen free radical in presenium rats. METHODS　The learning and memory function was determinated by Y-Maze; The contents of protein and MDA in cytoplasm and mitochondria were assayed by methods of Lowry and TBA respectively; The contents of GSH, GSSG, Mn-SOD and CAT in cytoplasm and mitochondria were assayed by spectroscopy,fluorescence spectroscopy, XO and UV spectroscopy respectively. RESULTS　The learning and memory function in presenium rats treated with HC（10 mg。kg^-1。d^-1×21 d, sc） decreased significantly, accompanied with increased levels of MDA and GSSG, and lowered levels of GSH, SOD and CAT. CONCLUSION　HC can induce the change of learning and memory via production of oxygen free radical.