The aim of this study was investigated the mediation role of forgiveness between big five personality and Psychological Well-Being in adolescents in Shiraz city. Participants were 328 high school students (148 boys, 180 girls) were selected by cluster sampling in Shiraz, Iran. Mean age of the students was 17.They completed three self-report instruments: Big – Five personality scale, Psychological Well-Being Inventory and Trait Forgivingness Scale. The path diagram of hypothetical model tested by regression analyses, according to recommended steps of Baron and Kenny (1986). Results showed that the Big – Five personality dimensions can predict forgiveness and Psychological Well-Being significantly. Also result indicated that Big – Five personality dimensions influence in Psychological Well-Being by mediating role forgiveness. Implications and suggestion for future studies are discussed