Abstract: OBJECTIVE To investigate the damage of di-(2-ethylhexyl) phthalate (DEHP) on the morphological ultrastructure of mouse testis and the protective effects of Blegent(compound Y523) on mouse spermatogonia and sertoli cells. METHODS Fifty-five male mice were randomly divided into three groups: DEHP, Y523 and control group. DEHP dissolved in soya oil was given at the dose of 0, 10, 20, 50 and 100 mg·kg^-1·d^-1 for 30 d by intragastric administration consecutively in DEHP group. Blegent at the dose of 1 000 mg was mixed with same account of soya oil and intragastric administrated consecutively for 30 d in Y523 group before DEHP intragastric administration repeated as that in DEHP group. The mice in control group were given a standard diet. Transmission electron microscopy was used to observe changes of testicular ultrastructure. RESULTS Compared with the control group, with increased dose of DEHP administrated in DEHP group, the spematogenic cell often showed collapsed cell membrane and loosened nucleoplasm. Few organelles and obvious vacuoles formation were visible in the cytoplasm under the electron microscopy. Seminiferous tubule cells decreased in number and even vanished. Collapsed cell membrane, concentrated nucleoplasm and apoptosis-like structure were also detected in the cytoplasm of sertoli cell. Compared with the DEHP group, the structural and morphological change of spematogenic and sertoli cell in Y523 group approximated to that in the DEHP group corresponded to increased dose of DEHP intragastric administrated but the increased count of organelle such as mitochodria and lysosome in the cytoplasm of sertoli cell were observed. CONCLUSION Intragastric administration of DEHP could lead to the ultrastructure changes of sertoli cell with oncosis or apoptosis and obvious vacuoles formation, decreased count of organelles in cytoplasm of spermatogonium. Blegent may protect and repair the damaged testis of mouse by mechanism of increasing the amount of mitochodria and lysosome in cytoplasm of sertoli cells.