<p>This study, grounded in the theoretical frameworks of social comparison and institutional trust, employs a multiple mediation model to elucidate the mediating mechanisms of social justice and social trust in the relationship between relative deprivation and mental health. Using data from 3777middle-aged and older adults in the Chinese General Social Survey, we conducted OLS regression and bootstrap analyses. The results demonstrate that relative deprivation among middle-aged and older adults not only is negatively correlated with mental health, but is also indirectly associated with mental health through two mediating variables: social justice and social trust. Furthermore, bootstrap analysis reveals a significant serial mediation pathway from relative deprivation through social justice to social trust, with an effect size of −0.002. These findings suggest that interventions targeting reduced relative deprivation, enhanced perceptions of social justice, and strengthened social trust may effectively improve mental health outcomes in this population.</p>