Abstract: Background and Objective: Metformin as an oral anti-diabetic drug is an attractive option for control of gestational diabetes. However, its safety during pregnancy needs further evaluation. This study aimed to evaluate the safety and efficacy of oral medication (metformin) in comparison to insulin as regard maternal and neonatal outcome. Materials and Methods: Comparative prospective randomized controlled study was carried out in Obstetrics and Gynaecology Department, Al-Azhar University hospital (New Damietta) during the period from January, 2017-October, 2018. Pregnant women diagnosed with gestational diabetes mellitus were included. The first group received insulin while second group received metformin. Both groups were compared as regard maternal and neonatal outcome. Results: About 106 patients were included. About 50 patients received insulin and 56 patients received metformin. There were statistically significant differences as regard mean fasting and post prandial blood glucose level (92.42±4.93, 129.82±7.88 vs. 86.88±5.02, 117.30±8.84) and mean birth weight ( 3.52±0.14 vs. 2.99±0.12) in insulin and metformin group, respectively. Also, increased CS rate (81.5% vs. 57.7%) between insulin and metformin group, respectively. Conclusion: It was concluded that Metformin is more effective in controlling mild GDM with comparable maternal and neonatal outcomes to insulin therapy.