Purpose: The purpose of this study was to investigate the effect of debriefing learning using peer feedback after blood transfusion nursing simulation practice. Methods: This study is a mixed method research to investigate the effect of debriefing using peer feedback on learning. The subjects of this study were third-year nursing students, and 23 of them were allocated to the control group and 19 to the experimental group. The experimental treatment was performed for about three hours, and the debriefing using peer feedback was not performed with the control group. The effect of the debriefing was measured in terms of the knowledge, attitude, and confidence in the performance with regard to blood transfusion nursing. The qualitative data about cognitive learning experience during the debriefing were analyzed. The quantitative data were analyzed by a t-test, a x² test, and a paired t-test by using IBM Statistics SPSS 19.0 software. Results: The results showed that the knowledge was significantly increased in both the control group and the experimental group (paired t=-6.411, p<.001; paired t=-5.759, p<.001), that the attitude toward the blood transfusion nursing was not significantly changed in both groups (paired t=-0.639, p=.530; paired t=-0.631, p=.536), and that the confidence in the performance was significantly increased in both groups (paired t=-5.124, p<.001; paired t=-4.747, p<.001). The qualitative data analysis of the cognitive learning experience during the debriefing showed that the content was divided into four subjects: “My errors are clearly seen as I reflect on myself,” “I can understand how to say and perform,” “I could make the knowledge my own by reviewing what I have done,” and “I could have see the big picture of nursing skills.” Conclusion:. The results of this study showed that the debriefing using peer feedback after the simulation had the learning effects of repeated learning and experiential learning of specific nursing skill, indicating that it is a useful education tool in nursing education.