Introduction: Vitamin D levels are known to be related to prevalence of allergy and infection in children. However, vitamin D levels in infants’ umbilical cord blood need to be investigated. Therefore, this study aimed to determine association between 25-hydroxyvitamin D [25(OH)D] levels and incidence of allergy and infection in children. Methods: A longitudinal study involving 38 full-term newborns was conducted. Serum 25(OH)D levels in infants’ umbilical cord and venous blood were measured at birth and six months, respectively. 25(OH)D levels were classified as insufficient (<20 ng/mL) and sufficient (>20 ng/mL). Parents filled out questionnaires about their children’s allergy and infection symptoms. Paired t-test was performed to compare the 25(OH)D levels at birth and at six months. Chisquared test was conducted to determine relationship between 25(OH)D levels and incidence of infection and allergy in children. Results: 25(OH)D levels in venous blood of 6-month-old infants were significantly higher than in umbilical cord blood (50.44±13.59 ng/mL vs. 20.70±6.60 ng/mL, p<0.001). In addition, 25(OH)D level insufficiency in umbilical cord blood was associated with infection (p<0.05). However, there was no incidence of allergy, and exclusive breastfeeding and sun exposure were not associated with vitamin D levels in 6-month-old infants. Conclusion: We conclude that 25(OH)D level insufficiency in umbilical cord blood was associated with incidence of infection in the first six months of life.