The aim of this research was to investigate the associations between attachment styles, mental well-being and psychological vulnerability. The sample comprised a total of 257 university students including 205 women (79.8%) and 52 men (20.2%). The ages of university students varied from 18 to 34 years [M[subscript age] = 21.37, SD = 2.13]. The Process Macro (Model 4) application was used to test the mediation analysis. According to mediation analysis findings, secure attachment style (ab = -0.20, SE = 0.05, 95% CI [-0.31, -0.09]), anxious-ambivalent attachment style (ab = 0.08, SE = 0.02, 95% CI [0.04, 0.13]), and avoidant attachment style (ab = 0.08, SE = 0.02, 95% CI [0.03, 0.14]) had significant indirect effects on psychological vulnerability. Additionally, mental well-being had full mediation role in the association between secure attachment style and psychological vulnerability, while mental well-being was determined to have partial mediation role in the associations between anxious-ambivalent and avoidant attachment styles with psychological vulnerability.