Purpose: This study was conducted to identify nurses’critical thinking disposition, self-leadership and clinical competency in small to medium sized hospitals less than 300beds. Methods: Data were collected using the questionnaire from 227 nurses in Incheon city and Gyeonggi province from March to April, 2017. The data were analyzed using t-test, ANOVA and Scheffé’s test to identify differences in critical thinking disposition, self-leadership and clinical competency. Pearson correlation coefficients were used to identify the correlation among the study variables, and multiple regression was used to identify factors contributing to clinical competency. Results: There were significant differences in critical thinking disposition according to age, marital status, clinical career, career in currently working department and education about leadership. Significant differences in self-leadership were identified according to marital status, work position, working department, work type, education about leadership, and turnover intention. Clinical competency was significantly different depending on age, education, monthly income, work position, career in currently working department, work type, education about critical thinking disposition and education about leadership. Clinical competency was positively correlated critical thinking disposition and self-leadership. Critical thinking deposition, monthly income and self-leadership explained 30.1% of clinical competency of nurses working in small to medium sized hospitals. Conclusion: The results of this study suggest that we need to improve nurses’critical thinking disposition, self-leadership, and the clinical competency.