PurposeWe aimed to investigate the role of platelet-to-lymphocyte ratio (PLR) in cognitive decline in patients with type 2 diabetes mellitus (T2DM).MethodsA total number of 261 T2DM patients were enrolled in this study. The T2DM patients were divided into two groups according to the median of PLR (PLR < 96.5, n = 130; PLR ≥ 96.5, n = 131). Cognitive impairment was defined as Mini-mental State Examination score ≤ 26. Student’s t test and Chi-square test were used to test the difference between the groups, and logistics regression analysis were performed to verify whether high PLR was an independent factor for cognitive impairment.ResultsT2DM patients with cognitive impairment had significantly higher PLR level when compared with the simple diabetes group (p = 0.003). Incidence of cognitive impairment was higher in the high PLR group, compared to low PLR group (p = 0.040). Multivariate logistic regression analysis suggested that PLR was a risk biomarker of cognitive decline in T2DM patients (odds ratio [OR] = 1.010, 95% CI: 1.001–1.018, p = 0.013).ConclusionsWe demonstrated that a higher PLR was associated with cognitive decline in T2DM patients. The PLR may help to identify high-risk patients in time and provide clues for further prevention of cognitive dysfunction in T2DM patients.