Abstract: The aim of the present study was to evaluate the possible protective role of olive oil on mammary carcinogenesis. Experimental studies can support epidemiologic data on the influence of some nutrients that can affect risk and prognosis of neoplastic lesions. In the present study, seventy two Sprague-dawley female rats 42 days old were equally divided in tree groups, being group C supplemented with olive oil (5%) and submitted to chemical carcinogenesis induction with 20 mg kg-1 of 7, 12-dimethylbenzanthracene (group B and C). At 150 days, all the animals were sacrificed and necropsy process was conducted. Animals from group A did not developed neoplastic lesions and group C showed significant differences on the number and volume of the neoplastic lesions when compared to animals from the group that was not supplemented with olive oil, it was also verified the absence of metastases in this group. The present data suggests a possible protective role of olive oil, due to its content of oleic acid and phenolic compounds, on growth and differentiation of mammary neoplastic lesions that should be confirmed on further investigation projects.