Objective:To measure the content of 25-hydroxyvitamin D in preterm infants, and to investigate factors contributing to it. Methods: A total of 100 infants that were born in Maternal and Child Health Hospital and the 3rd People＇s Hospital of Wuxi from 05/2012 to 09/2013 were selected as subjects, 50 of which were preterm infants and the other 50 were full-term. Basic situations of birth were recorded and subjects were divided into groups according to different purposes. 25-hydroxyvitamin D in preterm and full-term infants and their corresponding mothers were measured by enzyme-linked immunosorbent assay;calcium, phosphorus, alkaline phosphatase (ALP) were measured using conventional biochemical method;bone mineral density (BMD) values were measured by quantitative ultrasound (QUS). Results: ① 25-hydroxyvitamin D in preterm infants was significantly lower than that detected in full-term infants (P < 0.01). ② 25-hydroxyvitamin D of the preterm group A (28 w≤gestational age≤32 w) was significantly lower than those of the group B (32 w≤gestational age≤37 w), group C (37 w≤gestational age≤39 w) and group (39 w≤gestational age≤42 w) (both P < 0.01). Infants were also divided into 3 groups according to neonatal body weight. All pairwise comparision showed significant difference (both P < 0.01). ③Preterm infants were divided into 3 groups: the regular implement, sporadic implement, and no implement of 25-hydroxyvitamin D groups. All pairwise comparision of the three groups showed significant difference (P < 0.05);④25-hydroxyvitamin D level of preterm infants was positively correlated with gestational age and neonatal body weight (P < 0.05). However, in full-term infants, none of these factors showed significant correlation (P > 0.05). ⑤There was no significant difference in serum calcium, phosphorus, and ALP between preterm and full-term infants (P > 0.05). In the preterm group, 25-hydroxyvitamin D was negatively correlated with ALP (P < 0.01). ⑥BMD difference between preterm infants and full-term ones was significant (P < 0.01). BMD of preterm infants was positively linked to gestational age, neonatal body weight and 25-hydroxyvitamin D level (P < 0.05), and was negatively linked to alkaline phosphatase(P < 0.05). In full-term infants, BMD was significantly correlated with gestational age and 25-hydroxyvitamin D level(P < 0.05). Conclusion: ① 25-hydroxyvitamin D is significantly lower in preterm infants than that in full-term ones; ②Gestational age, birth weight, and vitamin D or calcium supplementation of the mother have great influence on 25-hydroxyvitamin D level of neonatal preterm infants.