Abstract: Objective To compare the acute haematological toxicity for patients treated with craniospinal irradiation (CSI) using helical tomotherapy (HT) and conventional radiotherapy (CRT). Methods We retrospectively analyzed the acute haematology data of 70 hospitalized patients treated with CSI. Patients were divided into helical tomotherapy group (HT, 14 cases) and conventional radiotherapy group(CRT, 56 cases). Myelosuppression of two groups were recorded and compared according to CTCAE v3.0. Difference was compared by χ2 test. Results The incidence of leucopenia, thrombocytopenia and decreased hemoglobin were 100%, 100%, 78.6% in HT group and 91.1%, 67.9%,32.1% in CRT group, respectively(P<0.05); moreover, the incidence at grade Ⅲ-Ⅳ were 85.7%, 50%, 14.2% in HT group and 35.8%, 10.7%, 0 in CRT group, respectively(P<0.05). There were 10.7%(6/56) patients in CRT group and 92.8%(10/14)patients in HT group were delayed radiotherapy due to myelosuppression (P<0.05). The average myelosuppression time was 11.5 d in HT group and 17.37 d in CRT group (P<0.05)．Myelosuppression was more serious in patients treated with induction chemotherapy than those without induction chemotherapy before radiotherapy. Conclusion HT shows more serious hematologic toxicity compared with CRT, which may relate to low dose exposure range for bone marrow and whole body, chemotherapy, etc. More attention and researches should be applied to the acute haematological toxicity of HT.