Background: The diffusion-weighted imaging (DWI) brain stem score (BSS) is an easy to use and can predict the clinical outcome of acute basilar artery occlusion (BAO) who underwent endovascular thrombectomy. The purpose of the current study was to validate its performance in Chinese acute BAO patients treated with mechanical thrombectomy. Methods: Fifty consecutive patients with acute BAO who received early magnetic resonance imaging and treated with mechanical thrombectomy in a single-center were included. Early ischemic damage on DWI was evaluated by applying BSS system. Receiver operating characteristic (ROC) curve analysis was used to evaluate the performance of the score system and multivariate logistic regression analysis was performed to identify predictor of clinical outcome. Results: Favorable outcomes were achieved in 38% patients (19 of 50 patients). Recanalization was successful in 92% patients (46 of 50 patients). Mortality rate was 26% (n = 13/50). In ROC curve analysis, the area under ROC curve of BSS .864 (95% confidence interval [CI], .738-.945) to predict favorable and .769 (95% CI, .628-.877) to predictor mortality. In logistic regression adjusted for age, baseline National Institute of Health Stroke Scale and time to puncture, DWI BSS <= 2 (odds ratio [OR], 12.416; 95% CI, 2.520-61.179; P = .002) and DWI BSS >3 (OR, 7.871; 95% CI, 1.353-45.797; P = .022) were the independent predictor for favorable outcome and mortality at 3 months respectively. Conclusions: The results of this study suggest that the DWI BSS can be used to predict clinical outcome in patients with acute BAO treated with mechanical thrombectomy at 3 months.