【Abstract】Objective To observe the effect of phycocyanin on improving immunity and reducing chemotherapy damage in patients with cancer during chemotherapy. Methods 60 cancer patients were divided into lowdose group, highdose group and blank control group according to the amount of phycocyanin. The white blood cell inhibition degree, the use times of recombinant human granulocyte stimulating factor injection, T cell subsets, toxic and side effects were monitored respectively. Results The incidence of moderate and severe myelosuppression in lowdose group, highdose group and blank control group was 5218%, 1765% and 90%, respectively. The incidence rate of highdose group was significantly lower than that of lowdose group. respectively, which were significantly lower in the experimental group than those in the blank control group (P＜001)/The ratio of CD＜8+ was significantly increased, which indicated that the patients taking phycocyanin during chemotherapy could positively regulate the immune state of the body; meanwhile, the grades of nausea, vomiting and hemocytopenia in the experimental group were lower than those in the blank control group. Conclusion Phycocyanin can resist bone marrow suppression during chemotherapy, improve immune function to a certain extent, and reduce the toxicity and side effects of chemotherapy.