Abstract: Radiation therapy is the main method for cancer,which began in the late 19 century.There are nearly 100 years of brachytherapy and ¹²⁵I seed implantation is one kind of it.¹²⁵I seed has low dose and irradiate continuously.It can be implantation repeatedly.Compared with external radiation therapy,it is highly conformal,much more effective with minimal damage and few complications in treating malignant tumors.In recent years,¹²⁵I implantation for malignant tumors has been widely used in China.It is an ideal local treatment.But we still do not know its mechanism,the dose are usually based on the external radiation therapy.Research and related basic experiments are not reported much at home and abroad.Now,we will review the recent progress in this area.