Many chemotherapeutic drugs were developed and contributed to the increase of cure rate of cancer, however severe side effect of these drugs is a major cause of poor quality of life of cancer patients. Effect of deer blood on cancer therapy was investigated in mouse tumor model. Deer blood itself was shown to have mild antitumor activity. However it has significant effect on the reduction of the side effects of chemotherapy. Deer blood recovered the reduction of WBC and platelet (myelotoxicity) during fluorouracil chemotherapy. Deer blood also recovered the increase of serum blood urea nitrogen (BUN; indicator of renal toxicity) and increase of serum amylase activity (AMY; indicator of pancreatic toxicity) almost to the control level during cisplatin chemotherapy. Fluorouracil and cisplatin are major chemotherapeutic drugs which are currently used in clinical cancer therapy, and the results strongly suggest that deer blood can be used for reducing the side effects and improving the quality of life during chemotherapy of cancer patients.