Abstract: AimTo determine whether 7-oxo-dehydroepiandrosterone (7-oxo-DHEA) can reverse the hypoimmunity in BALB/c mice exposed to chronic mild stress. MethodsA chronic mild stress animal model was established by subjecting BALB/c mice to a stressful regimen arranged in an unpredicted manner for 4 consecutive weeks. Immunological function alternations under chronic mild stress were assessed by lymphocytes proliferative response to mitogens and NK cell lysis activity test. ResultsThe studies showed the correlation between the state of depression and abnormalities in the immune response, such as a decrease of T lymphocytes proliferative response to Con A and suppression of cytotoxic of NK cell. Meanwhile, significant decrease of T₃ and T₄ levels was also observed. When stressed mice were daily given 7-oxo-DHEA 15 mg·kg－1, lymphocyte proliferative response and the NK cell activity were significantly enhanced and the decreased levels of T₃ and T₄ were restored in the stressed mice. Conclusion7-oxo-DHEA can improve the depressive symptoms and hypoimmunity of BALB/c mice induced by chronic mild stress as its parent DHEA.