Phenylketonuria is one of the few treatable hereditary metabolic disorders. We must strive for early diagnosis and treatment to avoid irreversible damage to the nervous system. Once diagnosed, active treatment should be given, and the younger the age at which treatment begins, the better. The treatment mainly uses a low-phenylalanine milk formula. Once the blood concentration is reduced to the ideal level, natural foods can gradually be added in small quantities, with breast milk being the preferred choice. For older infants and young children, milk, porridge, noodles, eggs, etc., can be added. The addition of food should follow the principle of low-protein and low-phenylalanine, with the amount and frequency depending on the phenylalanine concentration. Both high and low concentrations of phenylalanine can affect growth and development. Since each child's tolerance to phenylalanine varies, it is also necessary to regularly measure blood phenylalanine levels during dietary treatment and adjust the diet according to the specific conditions of the child.