Purpose <p>The platelet-to-white blood cell ratio (PWR) is a potential hematological indicator of dynamic changes in chronic inflammation. We aimed to investigate the association between the PWR and the risk of new-onset type 2 diabetes (T2D) in older adults.</p> Methods <p>This retrospective community-based cohort study included 7571 community-dwelling older adults without diabetes from Kunshan, Jiangsu, China, who underwent health check-ups between January 2018 and December 2023. The PWR was calculated as the platelet count divided by the white blood cell count. The primary outcome was new-onset T2D. Associations were assessed using Cox proportional hazards models to compute hazard ratios (HRs) and 95% confidence intervals (CIs).</p> Results <p>During follow-up, 773 incident T2D cases occurred, and higher baseline PWR was significantly associated with a lower risk of T2D. Participants in the highest PWR quartile had a 24.0% lower risk (HR 0.760, 95% CI 0.615–0.940, <i>P</i> = 0.011) compared to the lowest quartile. Restricted cubic spline analysis revealed an approximately linear, inverse dose-response relationship (P overall &lt; 0.001, P non-linear = 0.282). Subgroup and sensitivity analyses confirmed the robustness of this association.</p> Conclusions <p>A higher baseline PWR is associated with a reduced risk of new-onset T2D in older adults, suggesting its potential as a simple, cost-effective inflammatory biomarker for T2D risk assessment in this population.</p> Clinical trial number <p>Not applicable.</p>