This paper describes a thrombosis in the vena cava caudalis of a 15 year-old cat with ascites. Trauma and eventually feline enteric corona virus infection in the cat were not detected. In the intrahepatic region, a blockage of vena cava caudalis was brought to light by ultrasonographic imaging. An aspirate of abdominal fl uid revealed modified transudate. Liver enzyme levels were increased in the serum sample of the cat. The levels of total oxidant status (TOS) and total antioxidant status (TAS) were elevated in the peritoneal fluid. Liver protection diet with L-carnitine, diuretic therapy and antimicrobial drugs were administrated for treatment of the cat. During the continuous treatment, the amount of abdominal fluid decreased, but never completely absorbed. L-carnitine was administered to the cat during the time of treatment, and subsequently the levels of liver enzymes decreased. However, the cat died because of recurrent ascites and persistent thrombosis. In conclusion, ultrasonographic examination was very reliable, non-invasive and highly useful diagnostic method for BCS and L-carnitine has crucial effects on the quality of life, energy metabolism and liver enzyme levels. However, the blockage of the vena cava caudalis could not completely respond to medical treatment and thrombosis should be eliminated by surgical intervention.