Introduction: Asymptomatic hemorrhagic transformation (AHT) is a common complication in acute ischemic stroke (AIS) patients treated with endovascular therapy. However, whether AHT has impact on the functional outcome of this patient’s populations is unclear, especially in patients treated with endovascular thrombectomy (ET). In this study, we aim to evaluate the influence of AHT on the functional outcome of AIS patients treated with ET. Methods: This observational study based on a prospective registry study. AIS patients with anterior circulation large artery occlusion and underwent ET with second-generation stent retrievers (i.e., Solitaire FR and Trevo) were recruited. AHT was diagnosed by CT according to the Heidelberg Bleeding Clarification. Head CT was performed 12-24 hours and 5-7 days post-treatment. The primary outcome was functional outcome at 3 months post-treatment assessed by modified Rankin Scale (mRS). Results: One hundred and two consecutive AIS patients (aged 61.1 years old) were recruited. 39 patients (38.2%) had AHT on post-treatment CT. Patients with AHT were more likely to receive post-procedures sedation (69.2% vs. 23.8%, p <0.001). Less patients with AHT achieved favorable outcome (mRS<3) at 3 months follow up (35.9% vs. 61.9%, p =0.011). Compared with 7 of 63 subjects (11.1%) died in no AHT group, 14 of 39 subjects (35.9%) died in AHT group, which was significantly higher ( p =0.003). The median length of follow-up was 19 (IQR 3.5-32) months. In long-term follow up, less patients with AHT achieved favorable outcome (30.8% vs. 66.7%, p <0.001). 15 of 26 subjects (57.7%) died in AHT group, as compared with 8 of 50 subjects (16.0%) died in no AHT group, which was significant higher ( p <0.001). On multivariate analysis, AHT was an independent predictor for both short- and long-term functional outcome and mortality. Conclusions: In AIS patients undergoing ET with second-generation stent retrievers, AHT is associated with increased risk of poor outcome.