Purpose: The purpose of this study was to examine the effect of debriefing program applying patient safety analysis and comparison of knowledge and attitude toward patient safety. Method: A nested design of pretest-posttest control group was used with root cause analysis for debriefing. The participants were 58 undergraduate nursing students recruited from one university in Chungcheong province. They were assigned to either an experimental group (n=28 or a control group (n=30). A structured root cause analysis method for debriefing program offered to the experimental group whereas the control group did not receive any program. The data were analyzed using the PASW 23.0 program with χ2test, t-test, and ANOVA. Results: The participants who had participated in the root cause analysis in the debriefing showed significant difference (p < .001). Conclusion: The result of this study found that the root cause analysis method in the debriefing improved patient safety. Therefore, this program can be widely used in nursing curriculum because it leads to efficient debriefing and improves patient safety through root cause analysis.