Purpose: The purpose of this study was to evaluate the effects of a simulation based clinical reasoning practice program on clinical competence in nursing students. The program was based on the theoretical frameworks of simulation models and experiential learning theory. Methods: The program consisted of eight scenarios which includes three main symptoms (abdominal pain, changes in mental status, dyspnea), for improvement of clinical competencies in nursing students. A nonequivalent control group pretest-posttest design was used for evaluation of the effects of the program. Fifty-two junior nursing students in Y University participated in the experimental group (n=25) or control group (n=27). Critical thinking was measured using a self-administered questionnaire. Clinical judgment and clinical performance were measured by a rater using the Rubric. Descriptive analysis, t-test, Mann-Whitney U, Wilcoxon signed rank test was used for data analyses. Results: Clinical judgment and clinical performance increased in the experimental group, but there were no significant differences in critical thinking. Conclusion: Results indicate that the program developed in this study is a useful strategy to enhance clinical judgment and clinical performance in nursing students. However, the program did not significantly enhance critical thinking disposition, and further study is needed to measure integrated clinical competence including critical thinking skills.