Objective: To investigate whether vitamin A combined iron supplementation for preschool children resulting in improved changes of childrens infectious morbidity when compared with sole vitamin A or iron supplementation.Method: In this randomized,placebo-controlled and blinded field intervention trial, about 445 3-6.years old preschoolers were randomly selected from all eight kindergartens in the area.All subjects were randomly divided into four groups: sole vitamin A supplementation group (Group Ⅰ, a single oral dose of vitamin A about 200,000 units), sole iron supplement group (Group Ⅱ, daily oral supplement with the element iron 1-2 mg/kg/day for five days a week, lasting for 6 months) and the combined supplement of vitamin A and iron (Group Ⅲ) and administration no vitamin A and ferrous sulfate as placebo-control (Group Ⅳ).The morbidity of diarrhea and respiratory infection, were collected during supplementation.The symptoms recorded were respiratory-related illnesses (runny nose,cough, and sore throat), fever, skin rash, other illnesses, and diarrhea-related illnesses (diarrhea,vomiting, nausea, and stomach pain).Result: The groups were comparable concerning compliance and loss to follow-up.There was evidence of the lowest incidence rate of respiratory related illnesses (RRI) and fewest symptoms of runny nose, cough, and fever (RCF) for children in group Ⅲ compared with children in groups Ⅰ ,Ⅱ and Ⅳ (p<0.05).Moreover, despite the undistinguished incidence rate of vomiting, nausea, and stomach pain, the rate of diarrhea related illness was significantly lower for children in group Ⅲ than for those in groups Ⅰ ,Ⅱ and Ⅳ.The present data also indicated that the duration of respiratory and diarrhea-related illnesses in group Ⅲ was the shortest among the four intervention groups, but symptom duration of runny nose cough and fever,etc al showed no marked difference among groups.Conclusion: The beneficial effects on infectious morbidity over 6 mo, highlight the more potential of vitamin A combined iron supplementation for preschool children when compared with sole vitamin A or iron supplementation.