In this study, we firstly report inhibition of amyloid beta(42) (A beta(42)) fibrillation, which is related to the progression of Alzheimer's disease, by digestion using proteases, combined with A beta(42) isolation using an immunoaffinity membrane. Especially, digestion of A beta(42) with carboxypeptidase Y (CPY) is effective for the inhibition of A beta(42) fibrillation, indicating that carboxy-terminal digestion of A beta(42) is efficient for the prevention of its fibrillation. The combinational method of the immunoaffinity membrane with CPY digestion is applicable to suppress A beta(42) fibrillation.