Carnitine is a vitamin-like substance that regulates lipid metabolism and energy production. Carnitine homeostasis is mainly regulated by dietary intake and biosynthesis in the organs, including the skeletal muscle and the liver. Therefore, liver cirrhotic patients with reduced food intake, malnutrition, biosynthetic disorder, and poor storage capacity of carnitine in the skeletal muscle and liver are more likely to experience carnitine deficiency. In particular, liver cirrhotic patients with sarcopenia are at a high risk for developing carnitine deficiency. Carnitine deficiency impairs the important metabolic processes of the liver, such as gluconeogenesis, fatty acid metabolism, albumin biosynthesis, and ammonia detoxification by the urea cycle, and causes hypoalbuminemia and hyperammonemia. Carnitine deficiency should be suspected in liver cirrhotic patients with severe malaise, hepatic encephalopathy, sarcopenia, muscle cramps, and so on. Importantly, the blood carnitine level does not always decrease in patients with liver cirrhosis, and it sometimes exceeds the normal level. Therefore, patients with liver cirrhosis should be treated as if they are in a state of relative carnitine deficiency at the liver, skeletal muscle, and mitochondrial levels, even if the blood carnitine level is not decreased. Recent clinical trials have revealed the effectiveness of carnitine supplementation for the complications of liver cirrhosis, such as hepatic encephalopathy, sarcopenia, and muscle cramps. In conclusion, carnitine deficiency is not always rare in liver cirrhosis, and it requires constant attention in the daily medical care of this disease. Carnitine supplementation might be an important strategy for improving the quality of life of patients with liver cirrhosis.