beta-Defensins are small cationic molecules that have antimicrobial actions against bacteria, fungi and viruses and contribute to mucosal immune responses at epithelial sites. The female reproductive tract is an important site of defensin production. This study was conducted to determine the possible changes in proportions and localization of beta-defensin 1-4 in the rat uterus at the 1st, 3th, 5th, 10th and 15th days of postpartum and at the period of diestrus using immunohistochemical techniques. In the present study, it was determined that beta-defensin 1-4 were generally found in all structural components of the endometrium (luminal and glandular epithelium, stromal cells and blood vessels) in both the nucleus and the cytoplasm of cells during the involution period and diestrus. Suprisingly, immunoreaction of beta-defensin 2 was also observed in the lateral membrane of the luminal and glandular epithelial cells on the 10th day of involution and immunostaining of beta-defensin 4 was also localized in the apical membrane of the luminal and glandular epithelial cells. The current study demonstrated beta-defensin 1-4 immunoreactivities in the endothelium of blood vessels were stronger throughout the involution period. Although beta-defensins 2 and 3 were localized in both the nuclei and the cytoplasm of endothelial cells, beta-defensins 1 and 4 were present in only cytoplasm. These results show that the most component of rat endometrium expresses human beta-defensin 1-4 in a involution-dependent manner. Therefore it may be asserted that these molecules constitute a organised protection to prevent uterus from probable infections during the involution process.