Background: Adolescents with type 1 diabetes must make the transition to adult-oriented health care as part of their development. Transition care is a multi-year process begins early in adolescence to provide healthcare that is developmentally-appropriate for enhancing effective knowledge and self-management. The aim of this study was to evaluate the effect of transition care educational program on transitional readiness, self-efficacy and quality of life among adolescent with type 1 diabetes mellitus. Design: A quasi-experimental research design was utilized to accomplish the aim of this study. Setting: This study was conducted in the outpatient diabetes clinic at health insurance hospital affiliated to Egyptian Ministry of Health and population at Benha city. Subjects: A purposive sample of (60) adolescents with type 1diabetes mellitus were included in this study. Four tools were used for data collection: A structured interviewing questionnaire, transition readiness assessment tool, self-efficacy questionnaire and Pediatric quality of life inventory diabetes module. Results: There was a highly statistical significant difference in all mean scores of adolescents' transition readiness, self-efficacy and quality of life domains three months post-program and six months follow-up assessment compared with the pre-program phase. Conclusion: The transition care educational program was a good strategy in improving transition readiness, self-efficacy and quality of life among adolescents with type 1 diabetes mellitus. Recommendation: Continuous implementation of transitional care program for adolescents with type 1 diabetes mellitus with the importance of follow-up in order to assess its long-term effects.