BACKGROUND Leptin and its receptor play a role in several disease processes such as pancreatitis and heart disease. However, their association with gallbladder mucocele (GBM) in dogs has not been reported. OBJECTIVE To evaluate differences in the expression of leptin and leptin receptor between dogs with and without GBM. METHODS Twenty-five healthy dogs, including 9 laboratory beagle dogs, and 22 client-owned dogs with GBM. METHODS Serum leptin concentration was determined in blood samples of all dogs by ELISA. Canine gallbladder samples were collected from 9 dogs with GBM that underwent surgery for therapeutic purposes and from 9 healthy laboratory beagle dogs as a normal control group. Samples were analyzed for leptin and leptin receptor mRNA by real-time polymerase chain reaction. RESULTS Serum leptin concentration was significantly higher in dogs with GBM than in healthy dogs (medians of 7.03 and 2.18 ng/mL, respectively; P < .001). Patients with GBM that had undergone surgery had significantly higher serum leptin concentrations than those that had not (medians of 12.2 and 4.09 ng/mL, respectively; P = .001). However, no difference in serum leptin concentration was found between dogs with GBM with or without endocrinopathies. The mRNA expression levels of leptin and its receptor were significantly increased in the gallbladder tissues of dogs with GBM. CONCLUSIONS Dysregulation of leptin might be involved in the pathophysiology of GBM, and leptin concentrations might be associated with GBM severity.