Abstract Background: Metformin is a logical intervention assuming that the efficacy and safety of its use for pregnant patients are established. Aim of Study: To assess the efficacy of metformin in controlling gestational diabetes compared to insulin. Patients and Methods: This randomized controlled study was conducted on 214 patients with gestational diabetes recruited from the outpatient clinic of 6th of October Central Hospital during the period from October 2019 to April 2021. After fulfilling criteria of inclusion and exclusion, patients were randomly assigned to either groups of treatment with either metformin or insulin. Serial of blood glucose level was assessed at enrolment and at follow-up visits. The outcomes were fetal and maternal outcomes. Results: Fasting blood sugar and glycated hemoglobin were significantly lower (p < 0.001) in the metformin group compared to the insulin group. However, 2 hours postprandial blood sugar did not show significant differences (p=0.105) between the two groups. Additionally, Metformin was bene-ficial in reducing maternal weight gain and neonatal birth weight. Furthermore, neonates in the metformin-treated group suffered fewer rates of neonatal hypoglycemia and NICU admission. Conclusion: Metformin alone was as effective as insulin for controlling Gestational diabetes mellitus.