Background: Providing critical care to trauma patients is the responsibility of emergency nurses worldwide, with the aim of lowering injury-related mortality and disability. Unprofessional triage might have unfavorable effects. A critical care nurse should be well educated and skilled in emergency nursing care, emergency triage, and decision-making. Triage training is a crucial component of emergency nursing education.. Aim of study: The study aimed to evaluate the effect of educational guidelines on critical care nurses' performance regarding emergency triage. Design: A Quasi-experimental (pre, post-test design) used to achieve the aim of this study. Setting: The study was conducted in emergency care unit at Sohag University Hospital. Subjects: A convenient sample of 50 nurses who included all available nurses in the previous mentioned setting. Data collection tools: I: Nurses' Knowledge Assessment Questionnaire which included; demographic characteristics, and nurses' knowledge regarding emergency  triage,  II- Nurses' Triage Competencies Observational Checklists, and III- Nurses' Attitude Measuring Scale. Results: The study showed that, there were improvements in nurses' knowledge, attitude, and practice mean scores regarding emergency triage with a statistically significant difference detected between nurses' knowledge mean scores post- educational guidelines than pre- educational guidelines at P value < 0.001. also, there was a statistically significant correlation between total knowledge and attitude scores, total knowledge, and practice scores, total practices, and attitude regarding emergency triage pre and post- educational guidelines at p<0.001. Conclusion: The study findings concluded that educational guidelines have a positive effect on critical care nurses' performance regarding emergency triage. Also, there was a significant positive correlation between total level of knowledge and level of practice and attitude. Recommendation: On-going and regular in –services educational programs regarding emergency triage should be included in the critical care nurses' performance.