Purpose: This study was conducted to identify the professional competency of nurses working in emergency medical institutions that use the Korean Triage Acuity Scale (KTAS), and to identify factors that affect them. Methods: This study collected data from 105 nurses working in emergency medical institutions from June to August 2020. For data analysis, descriptive analysis, t-test, ANOVA, Pearson’s correlation coefficient, and multiple regression were performed using the SPSS 25.0 program. Results: As for the professional competency in triage, the higher the self-efficacy (β=0.58, p<.001), the more experience they have in triage-related education (β=0.30, p<.001), 2-4 years of clinical experience in emergency department (β=0.19, p=.002), in case of triage alone (β=0.24, p<.001), the higher the level of education a nurse has (β=0.19, p=.003), the higher the professional competency in triage. These variables explained professional competency in a total of 64.2% of the participants (F=38.30, p<.001). Conclusion: To improve nurses’ professional competence in triage, introducing manpower expansion, financial support, and the provision of appropriate places is suggested. In addition, it is necessary to repeatedly provide educational opportunities in an environment similar to actual clinical practice by developing various scenarios and introducing simulations and web-based formats.