Background: Increased rate of infections in diabetes mellitus (DM) is an accepted fact. Pathophysiologically, several tasks of the immune system could be involved including polymorphonuclear (PMN) functions.Objectives: The aim of this research was to evaluate the respiratory burst process of PMNs that is an essential part of phagocytosis, in children with DM.Patients and Methods: Fifty two children with insulin dependent diabetes and 29 non-diabetic children were enrolled in this cross sectional study from 2010 to 2011. Nitroblue tetrazolium (NBT) test was done on PMNs taken from their heparinized blood. The resultant data was analyzed by SPSS version 16. P values were considered significant when it was under 0.05.Results: Mean NBTs were 72.1 15.84 and 94.68 5.31 in diabetics and non-diabetics, respectively (P<0.001). Using Pearson correlation, there was no significant correlation between the NBT level and age, gender, duration of diabetes, daily insulin usage and blood HbA1C level.Conclusions: Compared to non-diabetics, respiratory burst process of polymorphonuclears is obviously decreased in diabetic children.This can explain one of the mechanisms involved in the increased rate of infections in DM.