The present study was conducted to determine the effect of maternal gestational diabetes on the Vitamin D levels of the mother and their newborns and to compare it with healthy mother-infant pairs. The study design was a Case Control study. It was conducted at the antenatal unit of Obstetrics and Neonatal unit of Pediatrics department of a tertiary care hospital in costal Karnataka. Consecutive sample of otherwise healthy pregnant women presenting with Gestational Diabetes Mellitus (GDM) and their healthy term neonates were taken as study group. The weight matched healthy mothers and their healthy term neonates were taken as controls. The blood samples of the mothers, at term and the cord blood samples of the neonates were collected for estimating the Vitamin D levels. Vitamin D levels in the cases and controls were the primary outcome measures. The mean value of Vitamin D levels in the GDM mothers was 10.74 ng/ml and in the mothers forming the control group was 23.53ng/ml (p value < 0.001). The mean value of Vitamin D levels in GDM babies was 8.47ng/ml and was 19.51ng/ml in the control (p value < 0.001). Comparison of Vitamin D levels of mothers and infants of both groups showed a positive correlation. GDM seems to exacerbate the Vitamin D deficiency in the mothers and their neonates.