Obesity is one of the most prevalent health problems in the canine population. This study aimed to evaluate the clinical usability of the systemic immune inflammation index (SII) in obese dogs. A total of 25 obese dogs compared with 10 normal-weight dogs. Complete blood counts, the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) were measured in all dogs. The SII was calculated with the neutrophil count × platelet count/lymphocyte count formula. C-reactive protein (CRP) concentrations were determined with dog-specific commercial ELİSA test kits. The obese group had statistically higher WBC, neut, PLT, and SII than the control group. However, no significant difference between the groups in NLR, PLR, and CRP concentration. Additionally, a positive correlation between SII and serum CRP was determined. To the best of our knowledge, this is the first study to demonstrate the SII levels in obese dogs. Nevertheless, considering no statistical difference between inflammatory parameters such as NLR, PLR, and CRP between the two groups, large-scale studies are needed to reveal the reason for this increase in SII in obese dogs and understand its clinical utility.