Background: Gestational Diabetes Mellitus is considered to be a significant problem among pregnant women in Egypt. Aim: To evaluate the effect of educational protocol to improve pregnant women practices about gestational diabetes mellitus. Design: A quasi-experimental design was used. Setting: The outpatient diabetic clinic at Zagazig university hospital. Sample: A purposive sample of eighty pregnant diabetic women. Tools: Two tools were used in the study, Tool (1): Contained two parts; (1) demographic characteristics, (2) History about reproductive profile during pregnancy, Tool (2): Included two parts, assessment of knowledge of pregnant women about DM, and assessment of practice of pregnant women about DM. Results: The mean age of the pregnant women were 32.04 ± 9.36 years, also it was revealed that the total knowledge scores improved from 31.35% to 58.20%, with a highly significant difference (p=0.0044) for the participants, additionally, the overall increase in adequate practices improved from 56 to 78.5% after the implementation of the protocol sessions, with a significant difference (p=0.0106). Conclusion: The implementation of educational protocol for pregnant women was effective and enhanced their practices, and knowledge regarding the gestational diabetes mellitus. Recommendation: The study recommended that further studies for pregnant women with gestational diabetes mellitus should be applied in all health care centers.