The objective of this study was to confirm the clinical utility of hemoglobin A1c (HbA1c) in identifying dogs at a high risk for diabetes. In this cross-sectional study, all the dogs were categorized into a control group and 3 experimental groups (overweight, elderly, and dogs with diseases that can contribute to diabetes). The control group included young and healthy dogs that visited veterinary clinics mainly for health checkups or neutering. The HbA1c concentration of all the dogs was estimated and compared between the control group and the experimental groups. The HbA1c level was significantly higher in the experimental groups than in the control group. In addition, a significant correlation was observed between the HbA1c concentration and all experimental variables. The HbA1c concentration was higher in the overweight group [mean, median: 3.94, 3.9; range (R): 3.5 to 4.3%], the elderly group [mean, median: 3.94, 3.9 (R: 3.5 to 4.3%)], and the disease group [mean, median: 3.99, 4.0 (R: 3.5 to 4.9%)] than in the control group [mean, median: 3.52, 3.6 (R: 2.9 to 3.8%)]. According to the results of this study, HbA1c can be used to evaluate high-risk groups for diabetes in the veterinary field, as in human medicine.