The main purpose of this study was to investigate the relationships between personality traits and happiness with religious orientation as a mediator. The sample consisted of 301 Shiraz university students (110 male and 191 female) selected by applying a cluster random sampling method. Participants completed three questioners: NEO-FFI or short personality inventory of Costa and Mc Crae (1992); Intrinsic-Extrinsic Religious Orientation Scale (IEROS, Allport & Ross, 1967); and The Oxford Happiness Inventory (OHI Argyle; Martin& Crossland, 1989). Results of multiple regression revealed that Extraversion, and Intrinsic religious orientation were positive predictors of happiness, in contrast to Neuroticism which predicted happiness negatively. Also results showed that Religion orientation played the mediation role between these relationships. This explanatory model is elaborated in the article.