Background: One of the most pervasive endocrinopathies and medical implications of pregnancy is gestational diabetes mellitus. Applying Roy's adaptation model can contribute to more physically and mentally healthy behaviors, appropriate disease management, fewer complications, and an overall higher quality of life. Aim: The study aimed to evaluate the effect  of Roy's adaptation model based intervention on healthy behaviors and quality of life among gestational diabetic women. Design: A quasi-experimental research design (two groups "control/study", ″pre –posttest″) was used to fulfill the study's aim. Setting: The study was carried at Obstetric and Gynecological Outpatient Clinic at Benha University Hospital in Benha City, Qaliobya governorate, Egypt. Sample: A purposive sample of pregnant women was selected from the above-mentioned study setting. Tools: A structured interviewing self-administered questionnaire, women's knowledge questionnaire, women's healthy behaviors questionnaire, Roy's adaptation model scale and diabetes quality of life questionnaire. Results: After implementation of Roy's adaptation model based intervention, the mean scores of healthy behaviors and diabetes quality of life among the study group were significantly higher than in the control group. There was a highly significant statistical positive correlation between total Roy's adaptation model scores and total scores of healthy behaviors and diabetes quality of life in both groups at Pre, 2 weeks and one-month post-intervention phases. Conclusion: The Roy's adaptation model based intervention for gestational diabetic women significantly improve knowledge, healthy behaviors and quality of life. Recommendations: Developing evidence-based intervention based on Roy's adaption model to provide more insight into the promotion of women's health and adaption related to gestational diabetes.