The article presents the results of clinical studies of domestic cats and dogs with diabetes mellitus on the background of obesity at the beginning and for a month of treatment. Domestic cats with diabetes were prescribed active exercise and industrial diet Royal Canin Diabetic Feline, dogs – Royal Canin Diabetic DS37. The portion size was determined according to the manufacturer's recommendations. Treatment of small animals for obesity, both alimentary and endocrine, preferably involves feeding food in limited quantities to cause controlled weight loss, as well as increased physical activity, which can provide additional energy expenditure. Successful weight loss can reduce the effects of comorbidities associated with obesity, such as improved mobility in osteoarthritis, increased insulin sensitivity and the reversal of other metabolic disorders, and improved quality of life. The main pathogenetic therapy for animals with diabetes for both domestic cats and dogs is the mandatory use of insulin. Researching the market of drugs in Ukraine, we chose the most affordable and effective veterinary drug – Caninsulin. The dose of insulin was selected individually for each animal by plotting a curve of blood glucose concentration over three days. At the beginning of treatment and at the end of the course, we conducted a comprehensive study of animals of both species. In cats, the general condition significantly improved as a result of treatment: only one animal remained depressed, the number of cases of hyporexia decreased, only 25.0 % of animals remained pale mucous membranes; temperature within the physiological norm; vomiting and bradycardia were not reported. A decrease in the rate of shortness of breath and drowsiness also indicates an improvement in the condition of cats with obesity due to diabetes. The improvement of the general condition of domestic dogs is evidenced by the restoration of the condition of the coat (about 4 times), the restoration of appetite in 66.7 %. Only one dog had anemia of the mucous membranes. Anxiety, bradycardia, hypothermia and itching disappeared completely. Within one month, there was a tendency to decrease the body weight of animals of both groups, but due to the insufficient duration of treatment, their fatness still remained excessive. Which indicates the need for further correction of the pathological condition.