Objective To study the localization and distribution of somatostatin in rat mammary gland.Method Immunohistochemical methods were used to detect somatostatin in mammary gland of virgin rats,on days 6,12,18 of pregnancy,and days 6,12,18 of lactation.Results Intense staining for somatostatin in cytoplasm of epithelial cells and in the secretory material at all stages mammary gland.Conclusion Somatostatin is located in the whole epithelial cells cytoplasm and the secretory material of rat mammary gland.