A 5-year-old female Chihuahua was presented for acute collapse. Laboratory examinations showed markedly elevated levels of hepatobiliary enzymes. Empiric antibiotic therapy for bacterial infection of the liver was ineffective. The clinical signs worsened with the development of hyponatremia with hypoosmolality and elevated urine sodium levels. The dog was suspected of having acute cholangiohepatitis associated with an immune-mediated disease. Subsequently, it was diagnosed with syndrome of inappropriate antidiuretic hormone secretion (SIADH) on the basis of the specific disease criteria. Further tests showed normal function of the adrenal and thyroid glands, and MRI and cerebrospinal fluid (CSF) analysis did not show any intracranial diseases. Immunosuppressive therapy and water restriction resolved the clinical signs and improved the SIADH in this dog. This case indicates that SIADH can occur concurrently with suspected immune-mediated liver disease in dogs.