An 88-year-old female was admitted to our hospital because of aphasia and right hemiplegia (NIHSS=26). Brain MRI and MRA revealed acute ischemic lesion of the left hemisphere and occlusion of the left internal cerebral artery (ICA), respectively. We diagnosed acute ischemic stroke owing to occlusion of the left ICA caused by cardiogenic embolization (CE) (due to atrial fibrillation [AF]) or Trousseau’s syndrome (TrS) (due to multiple myeloma), and immediately performed intravenous administration of alteplase and mechanical thrombectomy, which resulted in incomplete recanalization of left MCA. The initial D-dimer was slightly raised (2.25 µg/ml). The retrieved thrombi was white and fresh clot. Cardiac ultrasound, whole-body CT, and another test were normal, but D-dimer increased to 8.83 µg/ml over time in admission. Although it was difficult for us to diagnose if this cerebral embolism originated from TrS or CE because she had AF and MM, we finally diagnosed that this event happened due to TrS considering histopathological findings of the thrombi and a rise in D-dimer. So we concluded that it is important to observe pathology of thrombi even though a patient has AF.