A 2-year-old 4.0-kg female Shih Tzu with history of hematemesis and melena was referred to Veterinary Medical Teaching Hospital, Seoul national University for further evaluation and treatment. During physical examination, the dog revealed mild depression, dry mucous membrane and abdominal pain. Hematologic values were normal and serum chemical values showed increased serum bile acid (53.47 umol/l, preprandial), fasting serum ammonia concentration (184 g/dl), alanine transferase (98 U/L), alkaline phosphatase (871 U/L) and gamma glutamyl transpeptidase (21 U/L), and decreased blood urea nitrogen (4 mg/dl), total protein (4.1 g/dl) and albumin (1.2 g/dl). Microhepatica was shown in abdominal radiography. During the ultrasound examination, dilated tortuous vein communicating with caudal vena cava ws observed near the stomach. Intraoperative jejunal vein portography was performed during laparotomy to confirm the location and size of shunt vessel. According to history taking, physical examination, hematologic and serum chemical examination and radiographic study, it was diagnosed as single extrahepatic portosystemic shunt. The anomalous vessel (7 mm, o.d.) that enter the caudal vena cava from the left gastric vein, near the level of the diaphragm, was identified. A Ameroid constrictor (5 mm, i.d.) was applied to the shunting vessel near the caudal vena cava. Hematologic and serum chemical values recovered gradually and were revealed normal values 4 months after surgery. Four month after surgery serum bile acids concentrations were 0.56 $mu$mol/l (preprandial) and 18.45 umol/l (postprandial). Abdominal radiograph showed normal gastric axis and it revealed normal size of the liver. Fine texture and increased echogenecity of liver and enlargement of portal vein were shown in ultrasonography. Single extrahepatic portosystemic shunt might be treated surgically using Ameroid constrictor.