Abstract Objektive: This research conducted to determine the effect of positive psychotherapy-based psychoeducation (PPT) based psychoeducation given to individuals with mental illness on forgiveness and psychological well-being. Methods:The study completed in a randomized controlled manner with 120 individuals diagnosed with mental illness (60 experiments and 60 controls) who were treated in the psychiatry clinic of Turgut Özal Medical Center (TÖMC) between October 2021 and February 2023. Eight sessions of PPT based psychoeducation given to the experimental group in the study. No intervention made in the control group. Descriptive Characteristics Form, Heartland Forgiveness and Psychological Well-Being Scale used in the study. Results:In the analysis of the data, number, percentage, mean, standard deviation, chi-square, dependent and independent groups t-test was used. Forgiveness sub-dimension, which is one of the post-test scale sub-dimensions of the experimental group, and the total mean scores of the forgiveness scale found to be statistically significant (p<0.05). It was determined that the post-test forgiveness scale total score average and the forgiveness of others scale sub-dimension total score averages increased in the experimental group compared to the control group. It was determined that the total mean score of the experimental group post-test psychological well-being scale was statistically significant (p<0.05). Conclusion:It was determined that PPT based psychoeducationgiven to individuals with mental illness was effective in increasing the level of forgiveness and psychological well-being. Keywords: Forgiveness, positive psychotherapy, psychiatric nursing, psychoeducation, psychological well-being, mental illness