Gestational diabetes mellitus is a severe and neglected threat to maternal and child health. Aim of the study to assess Effect of educational program about Gestational Diabetes Mellitus on knowledge and reported practice among women at Assiut city. Materials and Method: design A quasi-experimental research (pre- post test) was conducted in antenatal care clinics. Sample: A convenient sample the total number was 365 women attended clinics setting of study the study was conducted at Ante- Natal Care clinics of Assiut city which serves the west sector and woman's Health Hospital, Assiut University Tools. two tools, structured interviewing questionnaire and follow- up sheet Results. The prevalence of GDM was found to be 3.4% among pregnant women's, there is a statistical significant difference between Pre-test and Post-test Knowledge level (p.v= 0.000) and there is a statistical significant difference between Practicing exercise and blood sugar analysis (p.v= 0.000) Conclusion. Knowledge of women's was improved after implementation program. Recommendations Antenatal health educational classes for all women to increase their awareness about the importance of early, proper screening and effective GDM management to improve their pregnancy outcomes.