The present study compared leptin, adiponectin, and thyroid hormone concentrations in normal and obese dogs, and evaluated the association between leptin and adiponectin concentrations and thyroid function. The serum leptin, adiponectin, thyroid-stimulating hormone (TSH), total thyroxine (tT4), free thyroxine (fT4), triiodothyronine (T3), and cortisol concentrations were measured in 18 normal dogs (body condition score [BCS]: 4-5/9) and 16 obese dogs (BCS: 8-9/9). Leptin and T3 concentrations were higher in the obese group than the normal weight group (p < 0.01 and p < 0.05, respectively). In both groups, the T3 and leptin concentrations were correlated (r = 0.370, p < 0.05), as were the TSH and fT4 and adiponectin concentrations (r = -0.373, p < 0.05 and r = 0.369, p < 0.05, respectively). In the normal weight group, the TSH and fT4 concentrations were correlated with the adiponectin concentrations (r = -0.528, p < 0.05 and r = 0.482, p < 0.05, respectively). The results of the present study suggest that leptin and T3 concentrations are significantly higher in obese dogs than normal weight dogs, and the serum T3 and leptin concentrations are positively correlated.