A 6-year-old, spayed female Cocker Spaniel was presented with generalized seborrhea sicca. Initially gallbladder mucocele (GM) was suggested by high liver enzyme activities and a stellate pattern in ultrasonography. There were no responses during 16 months of medical treatments for GM. Hormonal assay and histopathological findings were consistent with a diagnosis of hypothyroidism. Levothyroxine therapy led to rapid resolution of dermatologic, serum chemical and ultrasonographic abnormalities. This report describes serial changes of skin lesions, serum chemistry and ultrasonography in a dog with concurrent GM and hypothyroidism following treatment of hypothyroidism.