Breast cancer is one of the most common and letal cancers in all over the world. Since there have been significantimprovements in treatment of breast cancer, there is still a big need for alternative approaches. In this study, weaimed to investigate protective role of hydatid disease against breast cancer. Twenty Wistar rats were dividedinto two groups of 10 rats each Group I (control) and Group II. In Group II intraperitoneal hydatidosis wasperformed. Then DMBA was applied to mammary tissues of all rats. Immunohistochemistry studies for Ki-67and S-100 in the tumoral tissue sections of DMBA induced mammary tumor in rats were performed. TUNELAssay was used to detect apoptotic cells of tumoral tissue. In vivo anticancer activity testing was carried outby preventing the tumorigenesis by DMBA in mammary tissue of rats. The expressions of the Ki-67 and S-100protein decreased in rats who had Hydatid Disease (HD) (Group II), compared with the control rats (Group I).TUNEL positive cells were higher in rats with HD (Group II), compared with the control rats (Group I). In vivostudies showed that HD prevented the tumorigenesis by DMBA in mammary tissue of rats with 50 percent.Inthe light of the evidence the present study showed that HD may have chemopreventive effects on DMBA inducedbreast cancer.