Background: Clinical trials have shown that benefits of endovascular recanalization (EVT) for acute ischemic stroke patients with sizable penumbral tissues seems plausible even beyond 6 h after their last seen normal (LSN). Persistency of ischemic penumbra remains unclear in delayed periods. Methods: From a prospective stroke registry database, we identified 111 acute ischemic stroke patients who had internal carotid artery or middle cerebral artery occlusion with baseline National Institutes of Health Stroke Scale scores ≥6 points and arrived 6–12 h after LSN. Baseline information and functional outcomes were prospectively collected as a clinical registry. Attending physicians made treatment decisions for EVT based on the current guidelines and institutional protocols. MR image parameters, including the volume of diffusion-restricted lesions and mapping of the hypoperfused area, were quantified using automated commercial software. Binary logistic regression analysis models, with modified Rankin Scale (mRS) scores of 0–1 at 3 months after stroke included as a dependent variable, were constructed. Results: Between 6 and 12 h after onset, 58% had a mismatch ratio of ≥1.8 at baseline and 42% had favorable imaging profiles as determined by DEFUSE 2 study. After 9 h, there was a mismatch ratio of ≥1.8 in 47 and 38% favorable profiles. EVT was performed in 54% of cases. A 3-month mRS score of 0–1 was found in 19% (25% in EVT and 12% in medical treatment groups) of cases. EVT was associated with an increased OR of having a mRS score of 0–1 at 3 months after stroke (adjusted OR 7.59 [95% CI 1.28–61.60]). Conclusions: Penumbral tissues were persistent in a substantial proportion of anterior circulation occlusion cases 6–12 h after LSN. EVT at 6–12 h in a predominantly Asian cohort resulted in better outcomes.