Although many studies have evaluated the retrieved thrombus to assess the cause of stroke after mechanical thrombectomy for acute large vessel occlusion, the results remain controversial. We investigated the hypothesis that the histology of the retrieved thrombus is enhanced by mechanical thrombectomy devices.Thrombi were collected from consecutive patients who had undergone endovascular mechanical recanalization for large intracranial vessel occlusion. The mechanical thrombectomy device used was either an aspiration catheter or a stent retriever. The hematoxylin- and eosin-stained specimens were quantitatively analyzed with respect to the relative fractions of the main constituents (erythrocytes and fibrin). Clinical and radiological findings were also evaluated.Of 65 patients, an aspiration catheter was used in 27 and a stent retriever was used in 38. The presence of a preoperative susceptibility vessel sign on magnetic resonance imaging was not correlated with the percentage of erythrocytes. The thrombus cross-sectional area was larger in the aspiration group than stent group (P < 0.01). Conversely, the percentage of the fibrin component was higher in the stent group (P < 0.001). Interestingly, preoperative intravenous administration of recombinant tissue plasminogen activator reduced the thrombus cross-sectional area with a trend of increased percentage of fibrin and reduced percentage of erythrocyte in the stent group.The histological differences between the retrieved thrombi are enhanced by mechanical thrombectomy devices. Stent retrievers may crush the thrombus, which may have a synergistic effect with recombinant tissue plasminogen activator. The histology of the retrieved thrombi might be different from the original thrombi.