Abstract: Objective　To analyze serum 25(OH)D level and the influence factors in preterm infants. Methods　The data of serum 25(OH)D level in preterm infants born from July 2012 to June 2014 were retrospectively analyzed along with gestational age, gender, parity, delivery mode, birth season, birth weight, age of the mother and pregnancy complications. Results　Totally 325 cases were included and their average gestational age was 33.41±2.29 week, the ratio of male to  dna ycneicfied D nimativ fo ecnedicni ehT .L/lomn 71.61±43.73 saw level D)HO(52 mures egareva dna 1?23.1 saw elamef insufficiency in preterm infants was 37.8% and 41.8% respectively. Serum 25 (OH) D levels in preterm infants born in summer and autumn were higher than those born in winter and spring, and there was statistical difference (P<0.05). Logistic regression analysis showed that birth season and the mother's age may be the risk factors that influence serum 25 (OH) D levels in preterm infants. Conclusion　The incidence of vitamin D deficiency and insufficiency in preterm infants is high, and the factors affecting the level of vitamin D need to be further studied.