The aim of the study is to examine the mechanism through which the trait gratitude leads to life satisfaction. To this purpose, we studied the mediating role of positive and negative affect in the relationship between gratitude and life satisfaction. The participants in the study were 325 Romanian students (Mage= 20, 84; 234 males and 91 females) from public universities who completed three measures, namely for gratitude-Gratitude questionnaire-6 (GQ-6), for life satisfaction-Satisfaction with Life Scale (SWLS), and for positive and negative affect-Scale of Positive and Negative Experience (SPANE). The results show that the students who evince high gratitude tend to express higher positive affect and less negative affect. Structural equation modeling states that gratitude influences life satisfaction via positive and negative affect (χ²/df= 2, 35; GFI=. 89; CFI=. 90; RMSEA=. 066). The data analysis shows that female subjects with higher gratitude and higher positive affect evince higher life satisfaction than male subjects. The results contribute to the understanding of the way in which gratitude influences life satisfaction.