Abstract: AIM: To study the effect of glucocorticoids(GCOR) on intelligence in mice and its mechanism. METHODS: Immunosuppresion and decrease in intelligence of adult and old mice were induced by GCOR(sc, 4 mg·kg^-1, qd×28). Calcium fluoresence indicator Fura-2/AM was used to measure free intracellular calcium (Ca²⁺i). Programmed cell death(PCD) and apoptosis were measured by means of electron microscopy and flow cytometry. RESULTS: GCOR was shown to be immunosuppress and decrese intelligence as well as caused PCD of hippocampus in mature and old mice In vivo and in vitro . This increase of GCOR continued in the free intracellular calcium concentration (Ca²⁺i) of thymocytes and hippocampus and caused PCD of thymocytes. CONCLUSION: GCOR was shown to be immunosuppress and decrease in intelligence and PCD in thymocytes and hippocampus resulted in sustaining increase in Ca²⁺i which may be one of the main reasons for the decrease of immunity and intelligance of mice and the process of ageing and apoptosis.