Background <p>Socioeconomic status (SES) has been widely associated with accelerated aging. However, the causal mechanisms underlying this relationship remain poorly understood. This study utilizes genetic data to explore the causal effect of SES on biological aging, with a focus on the mediating role of adiposity traits by using Mendelian randomization (MR) analyses.</p> Method <p>We applied a two-step MR using largely genome-wide association study (GWAS) summary data from the UK Biobank to estimate the causal effect of SES on biological aging, as measured by BioAgeAccel and PhenoAgeAccel, and assessed the proportion of this effect mediated by adiposity traits.</p> Results <p>MR analyses demonstrated that genetically determined education (<i>β</i> = −0.38; 95% confidence interval [CI]: −0.48, −0.28) and household income (<i>β</i> = −0.41; 95% CI: −0.62, −0.20) showed negative associations with BioAgeAccel. Similarly, genetically determined education (<i>β</i> = −1.30; 95% CI: −1.56, −1.04), household income (<i>β</i> = −1.72; 95% CI: −2.28, −1.15), and occupational attainment (<i>β</i> = −0.50; 95% CI: −0.79, −0.22) were inversely associated with PhenoAgeAccel. Mediation analyses revealed that body mass index (BMI) and waist-to-hip ratio (WHR) mediated the effects of household income on BioAgeAccel, accounting for 23.73% and 20.79% of the total effect, respectively. For PhenoAgeAccel, the mediating effects of BMI and WHR ranged from 15.20% to 53.42% for education, household income, and occupational attainment, respectively.</p> Conclusions <p>Our findings provide robust genetic evidence that higher SES mitigates biological aging, with adiposity traits mediating a significant proportion of this effect. These results underscore the importance of addressing socioeconomic inequalities and implementing adiposity-related health interventions to counteract accelerated biological aging.</p>