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Amyloidosis is a heterogeneous group of diseases in which misfolding of extracellular proteins is the pathogenic factor. Light chain amyloidosis (AL) is the most common form of amyloidosis, and the causative proteins in AL are the immunoglobulin light chains produced by clonal plasma cells. Hemorrhagic events, ranging from mild subcutaneous hemorrhage to life-threatening bleeding, account for a significant proportion of morbidities and mortality in AL patients. Deficiency of factor X from deposition into amyloid fibrils has been reported to be the most common acquired factor deficiency in AL. We herein report 2 patients with acquired factor X deficiency in AL. A 55-yr-old woman with AL had a prolonged prothrombin time (PT) and an activated partial thromboplastin time (aPTT) of 2.51 International Normalized Ratio (INR) and 75.1 sec, respectively, which were corrected on mixing with normal plasma. Factor X activity was markedly decreased at 5%. The other patient was a 67-yr-old man with AL with a PT of 1.63 INR and an aPTT of 50.3 sec, which were corrected on mixing with normal plasma. Factor X activity was decreased at 17%. Neither of the patients had apparent hemorrhagic manifestations. Identification of acquired factor deficiency and timely coagulation tests are needed in the diagnostic workup and management in AL.