Abstract: Objective ： To observe the in ju ry of OS-732 cell lin e caused by rad iation combined fast neutron with photon. Methods ： We tested the cell su rvival rate ,cell death rate and colone forming rate of the OS-732 cell line after irrad iated by fast neutron,photon and the mixed beam (fast neutron plus photon) in different time. Results ： The killing effect were obvious in fast neutron alone group and the mixed beam in high proportion fast neutron group after the single dose radiation in 24,48 and 72 hours. Conclusions ： The killing effect was powerful to the OS-732 cell lin e in the fast neutron alone group and also the mixed beam in high proportion fast neutron group. These studies provide an experim ental research for the treatm ent of osteosarcoma.