The purpose of this study was to investigate the levels of end-of-life care competency; knowledge, attitudes, and experiences regarding advance directives; perceptions of good death; and end-of-life care obstacles and supportive behaviors among tertiary care nurses. Methods: The participants were 150 nurses at a tertiary hospital in Jinju, Korea. The data collected using a questionnaire were analyzed using descriptive statistics, the t-test, analysis of variance, Pearson correlation coefficients, and stepwise multiple regression in SPSS for Windows version 24.0. Results: The mean (±SD) score of end-of-life care competency was 3.63 (±0.53) on a 5-point scale. A significant difference in end-of-life care competency was found according to whether nurses had experienced the death of a family member or acquaintance (P=0.029). According to stepwise multiple regression analysis, the factors affecting end-of-life care competency were the frequency of end-of-life care supportive behaviors (β=0.38, P<0.001), experience with advance directives (β=0.29, P<0.001), and marriage (β=0.15, P=0.039). This model had an explanatory power of 27.9% (F=18.87, P <0.001). Conclusion: In order to improve nurses' end-of-life care competency, it is important to strengthen end-of-life care supportive behaviors by exposing nurses to those behaviors and providing frequent experience with advance directives.