The present invention relates to human neural stem cells (NSCs) transfected with a vector comprising a polynucleotide encoding human choline acetyltransferase (ChAT) and thereby stably expressing the human ChAT, a composition for treating Alzheimer disease or for improving a cognitive disorder comprising the human NSCs expressing a human ChAT. The present human NSCs genetically modified to express human ChAT, when transplanted into the brain of the animal AD model, successfully integrated into the host tissues and differentiated into the normal neuronal cells or glial cells. The instant genetically modified human NSCs stably express ChAT in the brain tissue of AD animal and thereby restore the acetylcholine level, and learning and memory function comparable to normal animal. The present genetically modified human NSCs expressing ChAT can be used for the treatment of AD as well as cognitive disorders due to other brain diseases and aging.