BACKGROUND: GNB3 C825T polymorphism affects G protein-coupled receptor signaling, influencing platelet function, inflammation, and cardiovascular risk. This study aimed to investigate the unknown effects of the GNB3 C825T polymorphism on recurrent stroke risk in large-artery atherosclerosis and its potential interaction with antiplatelet therapy. METHODS: Using the CNSR-III (Third China National Stroke Registry) data, we analyzed 1233 patients with large-artery atherosclerotic acute ischemic stroke enrolled within 72 hours of onset. Whole-genome sequencing was performed to identify the GNB3 C825T polymorphism. Cox regression analysis was used to assess its association with 1-year recurrent ischemic stroke after adjusting for vascular risk factors. Associations with antiplatelet regimens and mediating effects of inflammatory biomarkers in the overall cohort were also evaluated. RESULTS: Carriers of the GNB3 825T-allele (CT/TT, 72.7%) exhibited a significantly lower risk of 1-year recurrent ischemic stroke than noncarriers (adjusted hazard ratio, 0.67 [95% CI, 0.48-0.93]; P=0.02). In exploratory analyses, the association was observed in the aspirin monotherapy subgroup, but the interaction with aspirin use was not significant. Elevated baseline interleukin-6 partially attenuated this genetic protection in the overall cohort (mediation proportion, -9.82%; P=0.02). CONCLUSIONS: The GNB3 825T-allele was associated with a reduced risk of recurrent stroke in patients with large-artery atherosclerotic acute ischemic stroke. In exploratory analyses, this association was observed in the aspirin monotherapy subgroup; however, the formal interaction with aspirin use was not statistically significant. These findings support a potential prognostic role of the GNB3 C825T polymorphism and warrant further validation in independent cohorts.