Phenylketonuria is an autosomal recessive genetic disease, primarily due to a mutation in the phenylalanine hydroxylase gene which leads to reduced enzymatic activity, causing the accumulation of phenylalanine and its metabolites in the body, thereby leading to this disease. The main manifestations include developmental intellectual disabilities, light skin and hair pigmentation, and a musty urine odor. Once diagnosed, immediate treatment is necessary, mainly using a low-phenylalanine formula milk. Generally, when orally administering low-phenylalanine formula milk, it is essential to monitor the phenylalanine levels in the blood. Since each patient has a different tolerance level for phenylalanine, periodic determination of blood phenylalanine concentration is required in the dietary treatment. Such patients can only be treated long-term in this way; it is not curable nor can it be completely eradicated; treatment can only alleviate the symptoms and involves long-term administration of a low-phenylalanine diet.