The purpose of this research was to investigate the effect of Maekmoondong-tang(MMDT) on the activity of immune cell. The addition of MMDT(10 ㎍/㎖) enhanced the proliferation of cultured-splenocytes and thymocytes. And administration of MMDT(250, 500 ㎎/㎏) accelerated subpopulation of splenic T lymphocytes in BALB/c mice. In contrast, the treatment of the high concentration (500 ㎎/㎏)of MMDT were decreased thymic T lymphocytes. Administration of MMDT(250, 500 ㎎/㎏) eminently enhanced the production of IFN-γ. And MMDT did not affect the cell viability of Jurkat leukemia cells. These results suggest that MMDT have a immunoregulatory effect via enhanced cell mediated immunity