Background: Considering the importance of report writing and its problems, different teaching methods can be used to improve nurses' knowledge and performance, among which is peer teaching. This study aimed to determine the effect of peer teaching on the quality of report writing based on the nursing process. Materials and Methods: This quasi-experimental study examined 60 nurses working in the surgical and cardiac wards of Razavi Hospital in Mashhad during 2019. These wards randomly assigned to intervention (n = 30) and control (n = 30) groups. For 2 weeks, report writing teaching was implemented for the intervention group based on the nursing process through peer teaching. The control group routinely performed report writing. At the beginning and end of the study, we reviewed nursing reports of both groups using a valid and reliable checklist. Data were analyzed using two-way analysis of variance with repeated-measures analysis of variance. Results: Before the intervention, there was no significant difference between the two groups in terms of scores of report writing quality in structure, content dimensions, and the total scores (p > 0.05). After the intervention, the mean score changes were significantly higher in the structure (Mean Difference (MD) = 4.99, 95%CI: 1. 26–8.72, p < 0.010), content (MD = 8.11, 95%CI: 4.91–11.31, p < 0.001), and the total quality of report writing (MD = 7.54, CI: 4.56–10.53, p < 0.010) in the intervention group than the control group. Conclusions: Peer teaching improved the nurses' quality of report writing. The teaching planners are recommended to use this method to train nursing staff.