The aim was to describe a retrospective study of canine mammary tumors in Caracas, Venezuela. A retrospective study of cases diagnosed through biopsies in the diagnostic services private pathology in Caracas, Venezuela, during the years 2008–2014 was conducted. Tissue samples from mammary gland of canine patients were referred to three major veterinary clinics and veterinarians in private practice in the city of Caracas. Samples received in 10% formalin were processed by conventional histological methods and subsequently stained with hematoxylin-eosin and observed in the light microscope for histopathological diagnosis and classified by the system established by Goldschmidt et al. 2011 and finally a descriptive statistical analysis was performed. Mammary gland biopsies analyzed was a total of 878 biopsies. The 85% of breast tumors had malignant histological features characterized by marked anaplasia, nucleus hyperchromatic, loss of nuclear-cytoplasmic ratio, typical and atypical mitoses approximately more than 3 per field (40x) and of these 42% I present matrix formation osteoid, while 15% showed a benign histological pattern. The patter histological was hyperplasia 1%, adenoma 13%, carcinomas 27%, adenocarcinoma complex 41%, carcinoma mixed 17%. Histologic grading of canine mammary carcinomas and prognosis was: Grade I (23%), Grade II (53%) and Grade III 24%. These results suggest that mammary gland tumors in small animals accounted for the largest case series in the private diagnostic service during the years 2008–2014.