This research extended current positive psychological research by investigating the mediating effect of shyness on the association between optimism, psychological vulnerability and subjective well-being. Two hundred fifty-five volunteer university students (131 females and 124 males, mean age = 23.14) participated in the study. The structural equation modeling revealed shyness fully mediated the effect of psychological vulnerability on subjective well-being, while shyness partially mediated the effect of optimism on subjective well-being. Also, bootstrapping procedures confirmed that psychological vulnerability was indirectly associated with subjective well-being through shyness, whereas optimism was directly associated with subjective well-being. The implications for future studies and the limitations of the study were discussed in the context of the relevant literature.