Background: Phenylketonuria is an inherited autosomal recessive metabolic disorder that causes elevated blood phenylalanine concentrations. Aim of the study: To assess knowledge, attitude and reported practices of mother with phenylketonuria children at Hereditary Guideline Center in Assiut Governorate. Methods: Descriptive research design was used in this study. The total sample number of the studied sample was 360 mothers. Convenience sample was used Tools of the study: personal interview questionnaire which included Part (1) socio-demographic, Part (2) questions to determine knowledge, Part (3) attitude and Part(4) reported practices for mothers of phenylketonuria children. was used Results: slightly more two fifths (42.8%) of mothers aged 30->40 years, 31.7% of them had secondary education and 52.5% of them had low social class. According to their knowledge, 18.3% of the studied mothers had good knowledge regarding phenylketonuria, while 40% of them had fair knowledge and 41.7% had poor knowledge. Moreover, 81.4% of mothers had negative attitude toward phenylketonuria, and 76.1% of them had unsatisfactory practice. Conclusion: Most of the studied mothers had Poor knowledge, negative attitude and unsatisfactory practices Recommendations: Health education programs regarding phenylketonuria should be provided for mothers to improve their knowledge, attitude and practice.