PURPOSE: The purposes of study was to evaluate the effect of debriefing using reflection questions and writing on the critical thinking disposition, self-efficacy, and clinical judgement ability in simulation of post-operative care of abdominal surgery. METHODS: The research method was a nonequivalent control group no-synchronized design. The study period was from August 22 to 30, 2016. The subjects were comprised of 34 people in the experimental group and 36 in the control group. In a simulation session for post-operative care of abdominal surgery, the treatment of the experimental group was to debrief for 30 minutes using Lasater's reflection questions and writing. For the control group, a typical debriefing was conducted in the same environment. RESULTS: Critical thinking disposition, self-efficacy, and clinical judgement were significantly higher in the experimental group than the control group. CONCLUSION: To enhance the critical thinking disposition, self-efficacy, and clinical judgement of nursing students in simulation, it is recommended to debrief using reflection questions and writing.