Mechanical thrombectomy (MT) for acute ischemic stroke has become a standard therapy, and the recanalization rate has significantly improved. However, some cases of unsuccessful recanalization still occur. We aimed to clarify patient factors associated with unsuccessful recanalization after MT for acute ischemic stroke.This was a single-center, retrospective study of 119 consecutive patients with anterior circulation acute ischemic stroke who underwent MT at our hospital between April 2015 and March 2019. Successful recanalization after MT was defined as modified Treatment in Cerebral Ischemia (mTICI) grade 2b or 3, and unsuccessful recanalization was defined as mTICI grades 0-2a. Several factors were analyzed to assess their effect on recanalization rates.Successful recanalization was achieved in 88 patients (73.9%). The univariate analysis showed that female sex (38.6 vs. 67.7%, p = 0.007), a history of hypertension (53.4 vs. 83.9%, p = 0.003), and a longer time from groin puncture to recanalization (median 75 vs. 124 min, p < 0.001) were significantly associated with unsuccessful recanalization. The multivariate analysis confirmed that female sex (OR 3.18; 95% CI 1.12-9.02, p = 0.030), a history of hypertension (OR 4.84; 95% CI 1.32-17.8, p = 0.018), M2-3 occlusion (OR 4.26; 95% CI 1.36-13.3, p = 0.013), and the time from groin puncture to recanalization (per 10-min increase, OR 1.22; 95% CI 1.09-1.37, p < 0.001) were independently associated with unsuccessful recanalization.Female sex and a history of hypertension might be predictors of unsuccessful recanalization after MT for anterior circulation acute ischemic stroke. Further studies are needed to fully evaluate predictors of recanalization.