Background: Emergency services utilize a triage approach to rank patients according to the seriousness of their diagnoses. Triage is one of the abilities that a nurse working in an emergency room must possess. Aim: This study aims to examine the nurses' knowledge regarding triage and identify the variables that affect emergency nurses' knowledge of the triage systems. Methods: This cross-sectional descriptive study was performed from April to June 2021, on (48) nurses working in the emergency department. (ED) at Burridah central hospital in the Qassim region of Saudi Arabia. A self-administered questionnaire with non-probability purposive sampling was used to gather the data by sociodemographic data and triage knowledge. Results: The findings revealed that 68.8% were female and 45.8 % with a mean age of 31.79. Nurses revealed moderate levels of triage knowledge. Bachelor science nursing degree (p = 0.005, B= 10.659), years of experience for ≥5 years (p = 0.002, B =10.670), and training courses on triage (p = 0.001, B= 12.418) were affecting factors with statistically significant on emergency nurses' knowledge. Conclusions: Findings revealed that emergency nurses had a moderate level of triage knowledge and affecting factors of nurses' knowledge were qualification, years of experience, and training courses of triage Therefore, recommendations for training sessions and programs should be held and taken into account the connected increases in emergency nurses' knowledge of triage to improve the quality of nursing care and patient outcomes.