As obesity is a state of low-grade inflammation, we aimed to investigate the combined effect of high-fat diet and bacterial infection on β-cell function and insulin sensitivity in dogs. We used 20 healthy, male, mongrel dogs randomly divided into four groups: control group—healthy, non-obese dogs; infected group—non-obese dogs with experimentally induced infection (Staphylococcus intermedius); obese group—obese dogs (after 90 day high-fat diet) and obese-infected group—obese dogs with experimentally induced infection (Staphylococcus intermedius). To evaluate insulin sensitivity and β-cell function an intravenous glucose tolerance test (IVGTT) was performed. Plasma insulin increased in all group after glucose infusion. The lowest values were found in obese-infected group. Blood glucose also increased on 3 min after glucose infusion and then gradually decreased. In obese-infected group glucose concentration on 30 min was still significantly higher than initial levels, while in other groups glucose concentration returned to the initial values. The lowest rate of glucose elimination was found in infected group. In dogs of obese group and obese-infected group AUCins 0–60 min was lower compared to controls. AUCglucose 0–60 min values were lowest in infected group, while in obese-infectd group values were the highest. Levels of ∆I/∆G in dogs of obese-infected group were significantly lower compared to controls and infected group. In conclusion, these results reveal that infection in obese dogs leads to impaired glucose tolerance, which is result of impairment in both insulin secretion and insulin sensitivity.