The use of magnetic nanoparticles have been proposed as alternative techniques to assist breast cancer diagnosis and treatment. Peritumoral and intratumoral biodistribution of magnetic nanoparticles have been the main practical approaches, and the evaluation of breast tumor tissue marked selectively by magnetic nanoparticles has been not widely studied so far. The aim of this study was to evaluate the c-erbB-2 antigen in tissue of a breast cancer animal model as specific target for the use of magnetic nanoparticles coupled to specific Monoclonal Antibody (Mab). A breast cancer animal model was adapted and standardized in female rats. Tumor tissue was characterized histopathological and inmunohistochemical for cancer type and c-erbB-2 expression respectively. A bioconjugate was developed by the covalent union of fluorescent magnetic nanoparticles and anti c-erbB-2 Mab, and was used for incubation in two consecutive slides of breast cancer tissue acoordingly following conditions: (a) the c-erbB-2 receptor previously blocked by a primary antibody, and (b) the c-erbB-2 receptor non-blocked. Microscopy fluorescence was used to determine the selective marked of tumor tissue by the bioconjugate. Healthy breast tissue was used as negative control of selective labeling of the bioconjugate. The results show a well-differentiated fluorescent mark by magnetic nanoparticles in the non-blocked c-erbB-2 receptor breast cancer tissue condition, the observation suggests the use of the c-erbB-2 antigen as specific target to mark selectively breast tumor tissue by magnetic nanoparticles.