This study aimed to evaluate the possible relationship among UCP1, body weight, rectal temperature and lipid profile in the horse. Thirty clinically healthy Italian Saddle geldings (6–10 years old) were enrolled after the informed owners’ consent. All horses were blood sampled and their body weight and rectal temperatures were recorded. On the sera obtained after blood centrifugation the concentration of UCP1, total lipids, phospholipids, non-esterified fatty acids (NEFAs), triglycerides, total cholesterol, high density lipoproteins (HDLs), low density lipoproteins (LDLs) and very low density lipoprotein fraction (VLDLs) was evaluated. Pearson’s correlation analysis was applied to assess the possible relationship between serum UCP1 concentration and the values of body weight, rectal temperature and lipid parameters. Serum UCP1 concentration showed no correlation with body weight, rectal temperature, HDLs and LDLs values, whereas it correlated negatively with serum total lipids, phospholipids, NEFAs, total cholesterol, triglycerides and VLDLs values (p < 0.0001). The findings suggest that in the adult horse the role of UCP1 is linked to the lipid metabolism rather than to thermoregulation.