PURPOSE: The aim of this study was to evaluate differences of pre-post simulation training in problem solving ability, performance confidence, and critical thinking skill according to degree of nursing students' self-leadership. METHODS: This study was a descriptive survey using a self-report questionnaire. One hundred eighty nursing students participated in this study which programed a simulation scenario of pre-post operative patients' care. Descriptive statistics, paired t-test, ANCOVA with IBM SPSS 21.0 program were used for data analysis. RESULTS: After the simulation training, both the above-average subjects and below-average subjects in self-leadership significantly improved their problem-solving ability, performance confidence, and critical thinking skill. compared with their previous level. The subjects who rated above-average in self-leadership, improved their degree of problem-solving ability, performance confidence, and critical thinking skill significantly more than those who were below-average in self-leadership. CONCLUSION: Self-leadership of nursing students is an important element in effective simulation training.