Rhizoma Rehmanniae Preparata is a Chinese herbal tonic. The hemopoietic effects of Rhizoma Rehmanniae Preparata(4-time steamed Jihwang, 4-time steamed double dose Jihwang, 8-time steamed Jihwang, 8-time steamed double dose Jihwang) were examined using in vitro rat(SD) model. Cyclophosphamide(150 mg/kg) was injected into experimental groups and control group to induce bone marrow suppression. Oral administration of Rhizoma Rehmanniae Preparata suppressed hormone levels of $T_4;and;T_3$. Reticulocyte count was increased by the bone marrow suppression.