Purpose: The study was aimed to describe the relationships between ego-resilience, disaster experience, and core competencies among emergency room (ER) nurses. Methods: Data were collected from ER nurses in Incheon and Kyunggi province from May to June 2014. Data were analyzed with descriptive study, t-test, ANOVA, and Pearson``s correlation coefficient using SPSS/WIN 18.0 version. Results: Male respondents showed significantly higher ego-resilience than female respondents (t=-2.04, p=.043), and education (F=4.96, p=.002) and position (F=7.70, p=.001) were statistically significant. The differences in disaster experience was found in gender (t=-2.29, p=.023), age (F=4.25, p=.006), marital status (t=-2.02, p=.045), education (F=6.34, p<.001), religion (F=3.69, p=.015), and position (F=3.55, p=.031). Regarding core competencies for disaster nursing, age (F=7.80, p<.001), marital status (t=-3.00, p=.001), education (F=16.53, p<.001), career (F=5.40, p<.001), position (F=12.52, p<.001) were significantly different. Positive associations were found between core competencies for disaster nursing and ego-resilience (r=.66, p<.001), disaster experience and core competencies for disaster nursing (r=.52, p<.001), and disaster experience and ego-resilience (r=.33, p<.001). Conclusion: Core competencies were higher among ER nurses when they have higher ego-resilience, and more disaster experience. This finding suggests the need for improving ego-resilience among ER nurses. In addition, disaster education needs to be considered as a part of core nursing curriculum in college and clinical settings.