Abstract : Diabetes is the most common medical complication of pregnancy. Vitamin D deficiency which was initially considered only to influence bone metabolism, is now known to exert a wide spectrum of extra-skeletal effects. Vitamin D deficiency is closely associated with gestational diabetes mellitus, it also leads to adverse maternal and child outcome. Only few Indian studies are available in this regard. The present study was undertaken to find association of Serum Vitamin D status with gestational diabetes mellitus and other laboratory parameters. A single centred, institution based, prospective birth cohort study was carried out from January 2022 to December 2022 at the department of biochemistry, Jalpaiguri Government Medical College, West Bengal, India after obtaining ethical clearance. 150 patients with GDM and 150 patients with normal blood sugar were involved in this study. The data was tabulated in Microsoft Excel software and analysed with SPSS V.24 software. Mean age of patients with GDM was 23.45±5.361and mean age without GDM was 23.19±5.51. Mean BMI was higher in case (28.16±4.6) group compared to that in control group (24.63±4.1). Mean FBS was higher in case (117.85±6.7) group compared to that in control group (85.55±0.5), mean PPBS was also higher in case (175±1.4) group compared to that in control group (103.11±0.6). The mean serum vitamin D level was lower in case group case (17.43±0.8) compared to that in control group (27.14±1.07). Women with vitamin D deficiency have an increased risk of developing GDM and other complications as compared to those who had normal level of vitamin D.