The study aimed to determine the white blood cell (WBC) count and differential, the activity of digestive enzymes and the tissue level of some antioxidants in two Canidae species, which are closely related but differ in ecological characteristics, silver fox (Vulpes vulpes) and Arctic fox (V. lagopus), aged 0.5, 3.5 and 5.5 years. We demonstrated the species-specificity of some of the studied indices. Compared to silver foxes, Arctic foxes had higher activities of antioxidant enzymes, higher α-tocopherol content, lower glutathione level, higher stomach proteolytic and small intestine lipolytic activities, but lower pancreatic amylase activity. In silver foxes, the lymphocyte count decreased, while segmented neutrophil count increased with age, similarly to other aging mammals. Besides that, there was a minor age-related change in the activity of digestive enzymes and the tissue antioxidant defense in silver foxes. In contrast to red foxes, Arctic foxes demonstrated no significant age-related modifications of the WBC count and differential, but the proteolytic activity of the gastrointestinal tract changed in the proximal direction and the levels of antioxidants (especially α-tocopherol content) were significantly modified in the course of aging. Our results showed the asynchrony in the age-associated changes of the studied indices in farm-bred silver and Arctic foxes.