This study was purposed to evaluate the effects of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on hematopoietic reconstruction and survival in beagles exposed to mixed fission neutron and γ-ray. 13 beagles were unilaterally exposed to single dose of 2.3 Gy 90% neutrons. The experiments were divided into 3 groups: irradiation control group (no any treatment, n = 4), supportive care group (n = 5) and rhG-CSF plus supportive care group (n = 4, abbreviated as rhG-CSF group) in which the beagles were subcutaneously injected with 200 µg/kg of rhG-CSF early at half an hour and 24 hours post-irradiation respectively. The results showed that 2.3 Gy 90% neutron irradiation induced a severe acute radiation sickness of bone marrow type. The administration of rhG-CSF increased the survival rate from 60% in supportive care group to 100%. Twice injection of rhG-CSF in the first 24 hours reduced duration of neutropenia, enhanced neutrophil nadir and promoted neutrophil recovery when compared with control cohort administered clinical support. The number of colony-forming cells (CFU-GM, CFU-E, and BFU-E) in peripheral blood of rhG-CSF treated canines increased 2-to 5-fold relative to those of the supportive care group on day 3. All canines treated with rhG-CSF achieved hematopoietic reconstruction as evidenced by the pathological section of sternum while severe shortage of hemopoietic cells remained in the cohorts given supportive care alone. It is concluded that the combination of supportive care and high-dose rhG-CSF can accelerate hematopoietic recovery and enhance survival of dogs exposed to 2.3 Gy mixed neutron and gamma ray.