This study aimed to examine the mediating effect of optimism in the relationship between core self-evaluations and hardiness with life satisfaction. Based on a correlational design, 240 (78 male, 162 females) Islamic Azad University graduate students were selected via multistage sampling and responded to the Core Self-Evaluations Scale (CSEs; Judge, Erez, Bono & Thresen, 2003), the Personal Views Survey (PVS; Hardiness Institute, 1985), the Life Orientation Test-Revised (LOT-R; Seheier, Carver, & Bridges, 1994), and the Satisfaction With Life Scale (SWLS; Diener, Oishi & Lucas, 1985). Results indicated that the correlation between core self-evaluations, hardiness, optimism, and life satisfaction was positive and significant. Optimism played a mediating role in the relationship between core self-evaluations and hardiness with life satisfaction. These findings suggest the direct and indirect roles of core self-evaluations and hardiness in life satisfaction.