Background: Pulse oximeter is an essential monitoring and useful tool used in the intensive care unit although it has some pitfalls in it use. Aim: This study aimed to assess the factors contributing to neonatal nurses pitfalls during apply of pulse oximeter in neonatal intensive care unit. Design: A descriptive design was used in thisstudy. Setting: The study was conducted at neonatal intensive care units affiliated to Ain Shams University Hospitals and Zagazig Universty Hospital. Subject: A purposive sample composed of 80 nurses(50 nurses work at Ain Shams University Hospital and 30 nurses' worke at Zagazig University Hospital who provid care to neonates with puls oximeter. Tools of data collection: Involved A structured Interview Questionnaire sheet and Observational checklist to assessthe nurses practices used pulse oximeter in Neonatal intensive care unit. Results: revealed that, lessthan half of studied sample had good knowledge and less than one quarter of them had poor knowledge regarding to care of puls oximeter, while approximately more than half of studied sample had competent practice regarding to care of pulse oximeter. Illustrated a positive correlation between total knowledge of the studied neonatal nurses and their total practice regarding care of pulse oximeter. Conclusion: Based on results of the current study, it concluded that, factors contribute to neonatal nurse's pitfalls during application of pulse oximeter in neonatal intensive care unit the lack of studied nurse's knowledge about regarding care of pulse oximeter as well as lack of practice (incompetent) contributes to pitfulls. Recommendations: An orientation program should be prepared to help newly appointed nurses to acquire, develop their knowledge and practice to deal with neonatal nurse's care during application of pulse oximetry in neonatal intensive care unit