In order to study the mechanism of oligo-chitosan boosting survival rate with irradiated mice, the apoptosis number of borrow leukomo-nocyte cell, apoptosis related gene and P53 protein expression of the mice after 5 Gy γ-rays irradiation was investigated respectively. The cell apoptosis was analyzed by flow cytometry. Apoptosis related gene was determined by Real Time-Polymerase Chain Reaction (RT-PCR) and Western blot assay was used to examine the expression of P53. Compared with the control group, the results show that oligo-chitosan can either in-crease the survival rate or decrease the number of apoptosis and apoptosis related gene of Bax caspas-3, while Bc1-2 and Bcl-2/Bax ratio increase and the expression of P53 is restrained. It can be deduced that oligo-chitosan will influence the apoptosis related gene because of refraining the expression of P53 and leaded to shutdown the number of apoptosis, which then improve the survival rate of irradiated mice effectively.Cited