We studied the effect of Cepharanthin on bone marrow suppression induced by adjuvant chemotherapy in primary breast cancer patients in our hospital. The 36 patients with breast cancer were divided into two groups. Both groups were administered of MMC 20 mg intravenously on the day of radical operation. One group (23 patients) was administered of Cepharanthin 60 mg every day, but the other (13 patients) group was not administered. In the leukocyte count at 3 weeks after post operation, 82.6% (19 out of 23) of the patients who were administered cepharanthin kept more than 70% of pre-operation's leukocyte. On the other hand, only 46.1% (6 out of 13) of the patients who were not administered Cepharanthin kept more than 70% of pre-operation's leukocyte. The number of thrombocyte was not decreased in both groups. Side effects by Cepharanthin were not observed in this study.