Objective:To evaluate the clinical effect of mechanical ventilation in the prone position on children with pneumonia and atelectasis. Methods:Twenty-five patients with pneumonia and atelectasis admitted to Children’s Hospital Affiliated to Soochow University from Oct,2006 to Dec,2008,mechanically ventilated for hypoxemia,were divided into two groups:the supine position group and the prone position group. The ventilated mode was pressure control mode,regulating control pressure in order to keep expiratory tidal volume at 6~10 ml/kg level,setting inspiratory time(Ti)0.6~1.0 second,Respiratory rate(RR) 25~40 bpm,fraction of inspiratory oxygen(FiO2) 350~1000 ml/L,positive end-expiratory pressure(PEEP)5~12 cm H2O(1 cm H2O=0.098 kPa). Respiratory and circulatory indices,recovery time indicated by imaging,and ventilated time were assessed in the patients of two groups. Results:Oxygenation index(PaO2/FiO2) and pressure of artery oxygen(PaO2) of the prone position group were significantly higher than those in the supine position group(P < 0.05). Recovery time indicated by imaging and ventilated time of the prone position group were significantly less than those in the supine position group(P < 0.05),but there was no significant change in heart rate,blood pressure,pressure of artery CO2[Pa(CO2)],dynamic compliance,resistance of airway and peak of inspiratory pressure between the two groups. Conclusion:Mechanical ventilation in prone position can improve pulmonary gas exchange in children with pneumonia and atelectasis,and reduce recovery time indicated by imaging and ventilated time.