The aim of this retrospective study was to determine the incidence of canine and feline mammary tumors diagnosed in the Pathology Laboratory of Bornova Veterinary Control Institute in Izmir Province between January 2009 and December 2022, as well as to analyse the relationships between the age and breed characteristics of affected animals and the presence of mammary tumors. For this purpose, the available information regarding each mammary tumor case was collected from archive records. Dogs and cats with mammary tumors were divided into four age groups. All hematoxylin and eosin-stained slides of mammary tumors were histopathologically re-evaluated and classified. The study material consisted of 106 (35.81%) mammary tumor cases, of which 83 (37.55%) belonged to dogs and 23 (30.66%) to cats. The highest incidence of mammary tumors in both species was observed in the age group of 8 to 11 years. A statistically significant relationship was found between the incidences of mammary tumors according to the age groups and breeds in both species (p