Homoarginine (hArg) is an endogenous nonprotein amino acid, a pair of homologous amino acids to Arg, and is the synthetic substrate of NO synthesis. Recent studies have shown that hArg plays an important role in cardiovascular, liver, neurological function, and intrauterine growth restriction. However, compared with Arg, the application of hArg in human and animal research is still at an early stage, and its mechanism of action has not been fully proved. Therefore, the synthesis, transport and metabolic pathways of hArg were reviewed to provide theoretical support for the application of functional amino acids in animal production.