Aim of the study was to assess the nurses' knowledge versus performance regarding chest physiotherapy provided to children in pediatric intensive care units. Research Design: A descriptive research design was utilized. Settings: The study was conducted at Pediatric Intensive Care Units in Benha city in Benha University Hospital and Benha Pediatrics Specialized Hospital affiliated to Qualubia Governorate. Subjects: A purposive sample included fifty nurses and forty children selected from the previously mentioned settings. Tools: of data collection there were two tools, an observational checklist to assess performance and a structured interviewing questionnaire to assess knowledge. Results: the results revealed that more than three quarters of the studied nurses had unsatisfactory knowledge scores level and more than two thirds of the studied nurses are incompetent regarding performing chest physiotherapy. Conclusion: In Pediatric Intensive Care unit, the studied nurses had unsatisfactory knowledge and are incompetent in performing chest physiotherapy, there was highly statistical significant relation between nurses' performance and their qualification only. While there was highly statistical significant relation between nurses' knowledge and nurses' age, qualification and years of experience. Recommendations: Upgrading pediatric intensive care nurses' knowledge and performance regarding to chest physiotherapy through continuous in-service and in job training education program. Further studies about chest physiotherapeutic techniques performed by nurses on children in pediatric intensive care units are recommended at different settings.