High frequency oscillatory ventilation is considered one of the advanced modes of mechanical ventilation which is used for lung recruitment, avoids over distention, and does not rely on bulk flow for oxygenation and ventilation. This study Aimed to evaluate nurse's knowledge and practice about high frequency oscillatory ventilation in pediatric intensive care unit . Design: quasi experimental design was conducted on a sample of 54 nurse working in pediatric intensive care unit at Mansoura University Children Hospital. Data collection Tools :Two tools were used for data collection including questionnaire to evaluate nurse's knowledge about mechanical ventilation and high frequency oscillatory ventilation pre and post intervention, the second tool was an observational checklist to evaluate nurse's practice with high frequency oscillatory ventilation pre and post intervention. Results: more than half of the studied nurses had poor knowledge & the majority of them had poor practice about high frequency oscillatory ventilation pre intervention while post intervention both knowledge and practice was improved .Also, the studied nurses ' knowledge was affected by their experience and educational level. .Conclusion : all nurses had poor knowledge and practice pre intervention about high frequency oscillatory ventilation but improved after taking the course about high frequency oscillatory ventilation to be fifty four percent for knowledge &ninty eight percent for practice)Recommendations: it is recommended that continuous health educational program for all nurses about high frequency oscillatory ventilation and any new machines to improve their knowledge , practices and facilitate their dealing with the pediatric patient patients .