Brazilin, the main constitutent of Caesalpinia sappan, was examined for its immunomodulating activities in normal CBA mice. Mitogen induced proliferation and production of ConA induced T-cell growth factors (TCGF) of splenocytes were significantly reduced in brazilin treated group, cmpared to control group. It was also found that suppressor activities of splenocytes in brazilin treated group was significantly increased compared to those in normal control group.