Abstract Background: Vitamin D deficiency during pregnancy has important implications for the mother and infant. Adequate vitamin D concentrations during pregnancy are necessary to neonatal calcium homeostasis, bone maturation and mineralization. This study was designed to evaluate serum 25-OH vitamin D concentration in Bushehrian mothers and effect of vitamin D deficiency on pregnancy outcomes. Material and Methods: One hundred full-term pregnant women were recruited from a university hospital in Bushehr port, in spring & summer 2012. Maternal blood samples were collected on the day of delivery. Serum was assayed for 25-hydroxy vitamin D, calcium, phosphors and PTH. Vitamin D concentration of less than 20 ng/ml was considered as hypovitaminosis D. Results: Prevalence of vitamin D Deficiency was 76%. A significant direct correlation was seen between maternal serum calcium and birth weight of neonates (r= -0.31, P= 0.002). Mean serum level of vitamin D in mothers aged less than 30 years was significantly higher in comparison to less than 30 years mothers. (P= 0.24, 95% CI= 0.02-0.32). A significant direct correlation was seen between serum vitamin D level and parathormone (r= -0.33, P= 0.001). Conclusion: Consideration of adequate calcium and vitamin D intake during pregnancy is essential. Furthermore, it seems it is necessary to reconsider recommendation for vitamin D supplementation during pregnancy.