The main purpose of this study is to examine the mediator and moderator role of positive and negative affectivity variables on the relationship between optimism and life satisfaction in university students. 397 university students, ranging in age from 18 to 27 (M = 20.98), attending different departments of the Faculty of Education, at Pamukkale University in Turkey participated as subjects in the study. Data were collected by using PANAS, LOT, and SWLS. The relationship between optimism and satisfaction was partially mediated by both positive and negative affectivity. Hierarchical regression analysis indicated that positive and negative affectivity did not moderate the relationship between optimism and life satisfaction.