BACKGROUND Nurses play an effective role in the identification of donors and in the families' decision-making processes related to organ donation. It is recommended that nursing students be offered specific education regarding organ donation and transplantation. The aim of this study was to examine the effects of peer education on attitudes toward organ donation and the rate of attaining a donor card in undergraduate nursing students. METHODS This study was a quasi-experimental trial in a single group conducted between February 2016 and October 2016. Data were collected in 3 stages (pretest, posttest 1, and posttest 2) by using the Organ Donation Attitudes Scale. Data analysis was made with descriptive statistics, repeated measures analysis of variance, and the McNemar test. RESULTS The mean age of the participants was 21.63 ± 1.19 years. There was no statistically significant difference in students' attitudes toward organ donation after peer education (P > .05). The difference in the number of students having a donor card after peer education was highly significant (P < .05). CONCLUSIONS These study results showed that peer training did not positively change nursing students' attitudes toward organ donation but encouraged them to acquire a donor card and increased their knowledge of the organ donation system.