Inflammatory burden index (IBI) is a systemic inflammation indicator that reflects the inflammatory status. We aimed to investigate the prognostic value of IBI after endovascular thrombectomy (EVT) in patients with acute ischemic stroke.We enrolled patients treated with EVT from a multicenter cohort between June 2020 and December 2021. The IBI was calculated as C-reaction protein × neutrophil / lymphocyte count. The primary outcome was the unfavorable functional outcome (90-day modified Rankin scale score 3-6). C-statistics and net reclassification indexes were used to assess the predictive accuracy. Multivariable logistic regression models were used to investigate the association between IBI and unfavorable outcome.A total of 295 patients (mean age, 64.0 ± 12.8 years; male, 63.7%) were enrolled in this study. In multivariable models, higher IBI levels were associated with an increased risk of 90-day unfavorable outcome after EVT (per 1-SD: odds ratio, 1.754; 95% confidence interval, 1.241-2.587; P = 0.002). Restricted cubic spline curve displayed a linear relationship between the IBI level and 90-day unfavorable outcome (P for nonlinearity = 0.410). Besides, IBI was a more accurate biomarker for predicting unfavorable outcomes with the highest predictive accuracy and reclassification indexes.This study demonstrated that higher IBI was associated with an increased risk of 90-day unfavorable outcome in acute ischemic stroke treated with EVT.