In order to investigate the radioprotection property of water-soluble chitosan with low-molecular weight, sodium hydroxide eluting and oxidation degradation of chitosan with H,2,O,2, under HAc condition were used to prepare water-soluble low-molecular weight chitosan. MTT assay and flow cytometry (FCM) assay were performed to evaluate the cell survival rate, apoptosis and cell cycle alteration, respectively, after γ-rays irradiation. The results show that water-soluble low-molecular weight chitosan was successfully prepared, and the degree of deacetylation (D.D) of chitosan was increased from 79.3% to 94.1% while the molecular weight was decreased from 8.50×10,5, to 3.26×10,3, after treatment for 120 min. Low-molecular weight chitosan (LMWC) has good radio-protection effect to BRL cells from radiation damage induced by 4 Gy ,60,Co γ-rays in evidence of higher survival rate and lower SubG1 peek of the cells. After treatment with 50 μg/mL of LMWC, survival rate of BRL cells increased from 66.5%±0.19% to 87.5%±0.16% at 48 h (,p,<,0.05), the peak of SubG1 decreased from 51.9%±2.1% to 16.9%±1.3% at 24 h after 4 Gy ,60,Co γ-irradiation (,p,<,0.05).The results indicate that low molecular weight has excellent radio-protection effect to normal rat liver cell line (BRL).