Background: GDM increases the risk of pregnancy complications and adverse neonatal outcomes. Gestational diabetes mellitus has become an important high-risk pregnancy in the modern era. It is on the rise especially in South Asian countries like India. This study was designed to evaluating and comparing the maternal and fetal effects of metformin and insulin in GDM. Methods : The present hospital based prospective observational study was conducted in the Dept of Gynae and Obstetrics, Nil Ratan Sircar Medical College and Hospital, Kolkata, West Bengal, India between March 2020 to July 2021. Sample size for Metformin was 27 and for Insulin sample size was 29 after fulfilling the inclusion criteria, Statistical data were analysed by using Microsoft Excel and SPSS V.24 software. Results : In the present study 29 (51.8%) of the patients were treated with insulin and rest 27 (48.2%) of the patients were treated with metformin. Oligohydraminos was equally distributed among the patients of the two groups. proportion of Polyhydraminos among the patients treated with insulin (6.9%) which was higher than that of the patients treated with Metformin (3.8%). Proportion of Preterm delivery among the patients treated with insulin (17.2%) which was higher than that of the patients treated with Metformin (11.2%). Proportion of ND among the patients treated with insulin (48.2%) which was higher than that of the patients treated with Metformin (44.5%). Only 1 (3.4%) case of IUFD among the patients treated with insulin which was higher than that of the patients treated with Metformin (0.0%). Proportion of Neonatal hypoglycaemia of the babies among the patients treated with insulin (6.9%) which was lower than that of the patients treated with Metformin (11.1%). Conclusion : Metforrnin can be used as an alternative to insulin for the management of gestational diabetes mellitus.