Nutritional support may play an important role in management of liver cirrhosis (LC) associated with unresectable hepatocellular carcinoma (HCC). Total protein and albumin deteriorate in patients with LC undergoing trans-arterial chemoembolization (TACE). Therefore, in this study, we examined the hypothesis that short-term administration of branched-chain amino acids (BCAA) will prevent a fall in total protein and albumin in the perioperative period. The subjects were 56 patients who underwent TACE for HCC between 2004 and 2005 at Nagasaki University Hospital. The patients were randomly placed in the BCAA group (n = 28) or a control group (n = 28). The patients in the BCAA group consumed a snack containing 50 g of BCAA once a day at 10:00 pm starting 1 day before TACE and continuing until 2 weeks after TACE. A comparison of baseline and end point data showed greater decreases in the concentrations of total protein, albumin, cholinesterase, and total cholesterol and in the red blood cell count in the control group compared to the BCAA group. Ammonia levels decreased in the BCAA group and increased in the control group. Our findings indicate that a BCAA supplement taken orally as a late evening snack prevents suppression of liver function by TACE in patients with LC complicated with HCC during the 2-week period after TACE.