Background: Pregnancy during adolescent age is associated with poor neonatal care outcomes, which may burden the adolescent mothers and their families. Aim to delineate relationship of mother's age and family structure and knowledge about their newborn care. Methods: A descriptive comparative design of 396 mothers, 55 of them were adolescents, recruited from Post-partum Unit at Women's Health Hospital and neonatal intensive care unit at Children Hospital at Assiut University, Egypt, from January to June 2015. Results: comparison between adult and adolescent mothers revealed an unsatisfactory level of knowledge about newborn care, particularly regarding breast feeding, personal hygiene, and immunization. However, regarding family structure, it was found a significant difference between mothers live with nuclear against extended family regarding their knowledge about newborn immunization. Conclusion: Adolescent mothers have less knowledge about neonatal care, while mothers within a nuclear family have a satisfactory knowledge about neonatal care more than mothers within the extended family.