Radiation effects caused by 100kV/m and 400kV/m electromagnetic pulse (EMP) irradiations on mouse blood−testis barrier were studied by means of routine HE staining, Lanthanum traced electron microscope and injection of caudal vein with Evans Blue. The EMP irradiation of different dose rates damaged Sertoli's cell and blood−testis barrier of mouse testis in different levels. Severe injuries were observed with the 400kV/m irradiation group, with apoptosis and necrosis in a large quantity of the spermatogenic cells, shape and structural changes of the Sertoli's cells, and serious injuries to the blood−testis barrier, one day after the irradiation. The basal compartment separated from the adluminal compartment in most of the = 8 \* ROMAN VIII stage seminiferous epithelium, and a great number of apoptosis and necrosis spermatogenic cells were released into the cavities. Injuries of blood−testis barrier could be observed 21days after the 400kV/m irradiation. The injuries of 100kV/m irradiation groups were less severe than the 400kV/m groups, in which the damages to the Sertoli's cells, the seminiferous epithelium and blood−testis barrier recovered to some extent 14days after the irradiation. We conclude that EMP irradiation can damage mouse blood−testis barrier. The injuries, and the time for recovery, are related to EMP power intensity.