Background: High frequency oscillatory ventilation (HFOV) is a form of nonconventional ventilatory support employed for severe respiratory failure in children. Aim of the study: Was to compare the impact of early high frequency oscillatory ventilation (within 24 hours of endotracheal intubation) versus pressure controlled mechanical ventilation (P-CMV) and /or late high frequency oscillatory ventilation in patient with acute respiratory failure in prone position. Patients and Methods: Thirty-nine pediatric patients (19 males and 20 females) aged (2 to 156 months) were admitted in pediatric intensive care unit (PICU), Tanta University Hospital. They were categorized into 3 groups: Group I; 15 patients were monitored on early HFOV (within 24 hours from intubation). Group II; 18 patients were monitored on P-CMV. Group III; 6 patients were monitored on late HFOV (24 hours after intubation). All patients were subjected to scoring systems for Pediatric Risk for Mortality (PRISM III) and Sequential Organ Failure Assessment (SOFA) they were also monitored for [pulse oximetry, blood pressure, oxygenation Index, oxygenation saturation index, lung mechanics (compliance and resistance), ventilation parameters (HFOV and P-CMV) and Trans-Esophageal Doppler. Results: PP had superiority over SP in improvement of oxygenation / ventilation parameters demonstrated by the increased (PaO2, SaO2,pH) /decreased PaCO2, OI, OSI, FiO2 without harmful affection on HD. PP improve lung mechanics demonstrated by increased lung compliance with decreased airway resistance. PP can be safely applied in pediatrics. Conclusion: Early HFOV had superiority over CMV/late HFOV showed by the improvement in Oxygenation/ventilation.