Purpose: Very preterm infants, especially those 28 weeks of gestation are at high-risk of rickets; however, among moderate preterm infants, who were born at 32-33+6 weeks’ gestation, references of biochemical features related to vitamin D deficiency and calcium metabolism are very rare. The aim of study was to reveal the vitamin D status and relating factors in moderate preterm infants at birth. Methods: From February 2016 to February 2017, 63 infants born between 32 and 34 weeks’ gestation at CHA Bundang Medical Center were enrolled. Serum 25-hydroxyvitamin-D [25(OH)D] levels were determined from infant cord blood samples at birth. We examined the serum biochemical markers of infants and mothers at birth, maternal 25(OH)D levels, and perinatal variables. They were divided into two groups according to infant serum 25(OH)D concentration. We defined the vitamin D deficiency group as infant 25(OH)D concentrations 20 ng/mL. All data were collected prospectively with informed consent and analyzed by logistic regression analysis. Results: Among the total of 63 preterm infants, the serum 25(OH)D level was 17.9 ±7.4 ng/mL and 11.3±6.6 ng/mL in their mothers. The number of infants of serum 25(OH)D 20 ng/mL was 42 (66.7%). Maternal 25(OH)D concentrations (7.8±3.7 ng/mL vs. 18.3±5.4 ng/mL, P 0.001), the levels of infant serum calcium ( P=0.013), and the prevalence of birth during the summer and fall seasons (28.6% vs. 76.2%, P0.001) were lower in the vitamin D deficiency group as compared to the control group. Infant and maternal alkaline phosphatase (ALP) were higher in the vitamin D deficiency group (288±140 IU/L vs. 195±68 IU/L, P=0.001; 151±64 IU/L vs. 100±41 IU/L, P=0.001). There was no difference of gestational age, birth weight, the incidence of cesarean section, pregnancy induced hypertension and gestational diabetes mellitus between the two groups. In logistic regression analysis, maternal 25(OH)D and maternal ALP remained significant for infant vitamin D status. Conclusion: Vitamin D deficiency was prevalent in moderate preterm infants at birth. The maternal serum 25(OH)D and ALP evaluations will be helpful to predict the infant vitamin D status at birth. On the basis of our study results, we are able to design a larger-scale study for the optimal transitional fortifier/formula or enteral schedules for the moderate preterm infants.