Aim The effect of polysaccharide of spirulina on mouse myelosuppression induced by cyclophosphamide was studied. Methods Mice in the model, treatment groups Ⅰ and Ⅱ were given cyclophosphamide(ip 100 mg · kg- 1) for there days. At the same time mice in the treatment groups Ⅰ and Ⅱ were given ig spirulin 30 mg · kg-1 and 60 mg · kg-1 for ten days, while mice in the control group and model group were given ip 20 mg · kg-1 of NS. Peripheral blood and marrow cytometry, micromcelsus and chromosome aberration were analyed. Results In the dosages of 30 and 60 mg · kg-1 polysaccharide of spirulina, the polysaccharide of spirulina had perfect action on the perihemateikon and the function of bone hematoplast induced by cyclophosphamide(P ＜0.01) and antagonistic action on increase of bone cell micronuclsus(P＜0.05); The ratio of chromosome aberration in the treated group was lower compared with that in the model group. The inhibitory ratio was 51.2% and 62.5% in the treated groups Ⅰ and Ⅱ .Conclusion Polysaccharide of spirulina can perfect the hematoplast function of mice injured by cyclophosphamide.