Background: Hypertensive disorders in Pregnant obese women are associated with increased risk of maternal mortality and morbidity, metformin and aspirin have been reported to reduce the risk of them. Aim of the Work: to compare the effect of metformin versus low dose aspirin in prevention of hypertensive disorders in pregnant obese patients. Patients and Methods: During this study, 345 patients were assessed for eligibility and 300 patients were included in the study (100 in each group). First group received metformin started from 12 to 13 weeks till delivery at dose 1 g /day. Second group received Low dose aspirin at dose 150 mg daily from 12 to 13 weeks till delivery. Third group was the control group. In this study, we followed up each group at ANC visit and all patients were clinically examined. Results: Maternal weight gain during pregnancy at weeks 30 and 34 statistically was significantly lowest in metformin group (p value=0.016, <0.001) respectively, Hypertensive disorders of pregnancy, gestational hypertension and Preeclampsia were least frequent in metformin group, followed by aspirin group and most frequent in control group, the differences statistically were significant (p value<0.001, 0, 026, 0.019) respectively, marked lower limb edema was least frequent in metformin group and most frequent in control group, regarding preterm delivery was least frequent in metformin group, followed by aspirin group and most frequent in control group. Conclusion: Prophylactic therapy with a daily dose of 1.0 g of metformin in pregnant obese women without diabetes mellitus from 12 to 13 weeks of gestation until delivery was associated with less hypertensive disorders, less maternal gestational weight gain and less neonatal preterm delivery than that observed with aspirin and control groups.