PKU, known as phenylketonuria in Chinese, is an autosomal genetic disorder in which phenylalanine hydroxylase is deficient. It is more common in congenital disorders of amino acid metabolism and is characterized by the presence of large amounts of phenylketonate and other abnormal metabolites in the urine of children. Phenylalanine is an essential amino acid that is involved in the composition of many proteins, but cannot be synthesized in the body and needs to be consumed through supplementation with external substances. Phenylalanine is used in protein synthesis and is converted to tyrosine by phenylalanine hydroxylase, and then converted to dopamine, epinephrine, and norepinephrine by other enzymes. Phenylalanine is then excreted in the urine, manifesting itself as phenylalaninuria. Increased phenylalanine in children with phenylketonuria may affect the development of the central nervous system and lead to mental retardation. Some children may exhibit behavioral and personality abnormalities such as excitement, depression, and isolation. Low tyrosine content may affect melanin synthesis, resulting in lighter skin and hair color in children with phenylketonuria. Because the affected children metabolize more substances such as phenylpyruvic acid and phenyl lactic acid, which are excreted in large amounts from urine and sweat, a special ratty urine odor may appear on the body and in the urine of the affected children. Phenylketonuria is a hereditary disease and once diagnosed should be treated promptly and aggressively; the earlier the treatment, the better the prognosis. It is usually treated with low-phenylalanine formula, and when the blood phenylalanine concentration of the child drops to the ideal concentration, a small amount of natural diet can be added gradually. Children with poor dietary treatment can be treated with drugs such as salbutamol and tetrahydrobiopterin. Adult female patients should strictly control their blood phenylalanine levels before pregnancy to avoid the effects of hyperphenylalaninemia on the fetus.