Mouth care has a crucial role in preventing mucositis in pediatric patients who admitted to pediatric intensive care unit and undergoing mechanical ventilation. Aim: was aimed to assess oral cavity for children undergoing mechanical ventilated at Pediatric Intensive Care Unit. Subjects and method: A descriptive research design was used. The study were included 60 children (>6 years age) admitted at PICU undergoing mechanical ventilation. Tools: Data collection tools included: Socio-demographic characteristic and clinical data structured questionnaire, and oral cavity assessment tool. Results: It was found that most frequently occurring risk factors of mucositis among studied children were fever, drugs and malnutrition (66.7% & 23.3% & 20.0%) respectively and 63.3% of the studied children had moderate oral mucositis while quarter of them had severe oral mucositis. Conclusion: Children undergoing mechanical ventilation at the pediatric intensive care unit had moderate and severe oral mucositis. Recommendations: The use of an oral cavity assessment instrument is suggested for the early detection of oral infection for every patient and instruct nurses for using proper mouth care.