Carnitine and acylcarnitines are fundamental compounds for fatty acids metabolism. They widely exist in animals, plants and some microorganisms. Carnitine ranges from 0.2 to 6 mmol/kg in animal tissues, especially high in the heart and skeletal muscle. With methionine and lysine from protein degradation as precursors, L-Carnitine are synthesized in kidney, liver and brain of organisms. Through the circulation, carnitine and acylcarnitines are transported to other tissues to fulfill their roles. Meat, fish and dairy products are the main source of carnitine.