Objective To investigate the relationship between vitamin D（VitD）deficiency and respiratory infections in children.Method 80 cases of child patients were selected as the patient group who were received in Fengman District Hospital of Maternal and Child Health from January 2010 to June 2013 and met the diagnostic criteria for recurrent respiratory infections.50 cases of healthy children were randomly selected as the control group.The levels of serum 25-hydroxy vitamin D3（25-OH-VD3）were compared between the two groups.The patient group were randomly divided into the conventional therapy group and VitD supplement group

40 cases in each.The conventional therapy group was given antibiotic and symptomatic treatments and the VitD supplement group was received oral alfacalcidol supplement VitD under the treatment for the conventional therapy group.Three months later

the levels of serum 25-OH-VD3 were rechecked.During six-month follow-ups

the relapse number of recurrent respiratory infections was recorded.Results Before the treatment

the level of serum 25-OH-VD3 in the patient group was（23.41±7.13）nmol/L

significantly lower than that of the control group with the level of（76.23±8.90）nmol/L（P<0.05）.After three months of treatment

there was almost no significant change of serum 25-OH-VD3 level in the conventional therapy group but serum 25-OH-DV3 level in the VitD supplement group increased from（23.29±6.15）nmol/L to（58.95±10.87）nmol/L and there was a significant difference（P<0.05）.After six months of follow-ups

the relapse number of respiratory infections in the VitD supplement group was significantly less than the conventional therapy group（P<0.05）.Conclusion VitD supplement can significantly improve the level of serum 25-OHVD3 in children with respiratory infections and reduce the relapse number of respiratory infections.