Disclosed is use of an antibody or antigen-binding fragment thereof that specifically binds to an acid sphingomyelinase (ASM) protein, wherein the antibody or antigen-binding fragment thereof specifically binds to an ASM protein with high binding affinity, significantly inhibits the activity of an ASM protein present in the cellular membrane, and shows effects of improving cognitive memory, inhibiting ASM protein activity, inhibiting the accumulation of amyloid-β and tau proteins, and inhibiting the production of neuroinflammation even without toxicity in Alzheimer's disease animal models, and thus can be advantageously used in the treatment of a brain disease.