Background:  Type 1 Diabetes (T1D) is one of the most common chronic illnesses affecting school-age children. If not appropriately managed, T1D can drastically affect a student's ability to experience academic success. Diabetes self-care is particularly challenging for children. Aim: To assess preparatory school students' knowledge and reported practices about type1 diabetes mellitus. Design: A cross sectional research. Setting: the study was conducted in preparatory schools, the Aswan City. Subjects:  purposive sample of 99 students diagnosed with diabetes.  Tool (I): Structured interviewing questionnaire include 2 parts: First part: Personal characteristics of students and their parents, and medical history of diabetic students.  Second part: Students' knowledge about DM. Tool (II): Reported check list for students' regarding diabetic self-care practice. Results: More than half of students had good knowledge about diabetes, while slightly two thirds of them had unsatisfactory reported practice about diabetic self-care. Conclusion: study confirmed that there was positive correlation between knowledge and reported practices scores with highly statistical significant association.  Recommendations:  Health education programs and training courses should be developed and implemented for students to increase their awareness, attitude and practice about diabetes mellitus.