Circumanal gland (CG) tumors are common neoplasms of older dogs. Of these, only circumanal gland carcinomas show clear metastatic potential, and even so metastases seem to be uncommon. Epithelial-mesenchymal transition (EMT) is a process that facilitates the initial steps of metastasis, and to date it has not been systematically investigated in CG tumors. Insight into the occurrence of this process would be a valuable asset in understanding the biology of these tumors. To test the occurrence of EMT we used three immunohistochemical markers that alter their expression in this process, namely – E-cadherin, N-cadherin, and matrix metalloproteinase-9 (MMP-9). Additionally, we used the Ki-67 marker of proliferation. The samples used consisted of 15 adenomas, 11 epitheliomas, 21 well-differentiated carcinomas, seven poorly differentiated carcinomas, and ten samples of normal CG. The results of N-cadherin were negative for all samples. E-cadherin was highly expressed in all groups, but was slightly lower in semi-malignant and malignant tumors; MMP-9 marking was generally very low, but significantly higher in semi-malignant or malignant tumors when compared to benign or non-neoplastic CG. The index of proliferation (Ki-67) was significantly higher for semi-malignant or malignant CG tumors when compared to benign CG tumors or normal CG. These results show that with an increase in the histologic malignancy of these tumors there is a slight drop in E-cadherin, a slight rise in MMP-9, and a significant increase in Ki-67. Therefore, these results suggest the possibility that EMT occurs within the malignant or even semi-malignant forms of CG tumors, but probably as a rare and late event. Further studies are needed to prove or disprove these statements.