Canine mammary tumors represent one of the leading malignant pathology in female dogs, displaying the importance of efficient therapeutic findings, beside the golden standard surgery, able to limit the development of the disease. Studies in human cancers demonstrated that Doxorubicin presents a good effect in different biological processes like apoptosis, autophagy, cell cycle, cell invasion and epithelial to mesenchymal transition. Our study following the effects of Doxorubicin on two canine mammary cancer cell lines P114 and CMT-U27, showing an inhibitory effect in cell proliferation and an expression alteration of the EMT related genes.