The experiment was undertaken to evaluate the effects of active immunization against the gonadotropin releasing hormone agonist（GnRHa） on the expression and immuno-localization of FSHR in uteri,as well as uterine development in the ewes.Forty two ewes (Ovis aries),five-to-six months old,were randomly assigned into six groups (n=7).The animals in the experimental groups EG-Ⅰ,EG-Ⅱ and EG-Ⅲ were subcutaneously injected with 200 μg,300 μg and 400 μg alarelin antigens twice (on day 0 and 14),respectively,in groups EG-Ⅳ and EG-Ⅴ were subcutaneously injected with 200 μg and 300 μg alarelin antigens four times (on day 0,7,14 and 21),respectively and in control group (CG) were injected subcutaneously with 2.0 mL solvent twice (on day 0 and 7).The samples of the uterine horns of each ewe were collected aseptically on day 70 after killed by bloodletting from carotid.The FSHR distribution in the uteri was studied by the methods of Immunohistochemistry SP (streptomyces avidin- peroxidase) and image analysis,the mirostructure and ultrastructure changes of the uteri were observed under the optical and electron microscope,respectively and the expression of FSHR was detected by Western blot.The results showed that the expression of FSHR increased with the increasing of alarelin dose and injection times and the expression levels of FSHR in EG-Ⅲ and EG-Ⅴ were significantly higher than (P＜0.01) in CG.The FSHR were predominantly concentrated in the cytoplasm and nuclei of the uterine endometrial cells and glandular epithelium cells.The gray values of microscopy images in EG-Ⅰ,EG-Ⅱ and EG-Ⅲ increased gradually and were significantly higher in EG-Ⅲ and EG-Ⅴ than in CG (P<0.01).The uterine weights,endometrial epithelium thickness (EET) and uterine wall thickness (UWT) in all experimental groups reduced and were significantly lower in EG-Ⅲ and EG-Ⅴ than in CG (P<0.05).The uterine cavities and glandular lumen volumes narrowed,and the uterine wall became clearly thinner in all experimental groups.The quantities of mitochondria and mitochondria cristaes decreased and the microvilli became shorter,especially in EG-Ⅲ.In conclusion,alarelin active immunity enhanced distribution of FSHR,promoted the expression of FSHR protein in the uteri of the ewes,changed the mirostructure and ultrastructure of the uteri,inhibited the uterine development of ewes,and especially suppressed the growth of uterine endometrium.