This study aimed to investigate the neurotoxicity of exosomes to cultured neuroblastoma and neurons in vitro and to mature and newborn neurons in the hippocampus in vivo. Recent in vitro and in vivo studies have shown that exosomes, small membranous vesicles secreted from many cell types, contain pathogenic proteins including full-length amyloid precursor protein (flAPP) and amyloid precursor protein (APP) metabolites. However, the function of these exosomes in Alzheimer disease (AD) has not been much explored. In the present study, exosomes were harvested from the conditioned medium of HEK293-APP Swe/Ind cells and injected into the hippocampal dentate gyrus region via a stereotactic method to detect their effects on the neuronal survival in vivo. These exosomes containing pathogenic proteins showed high neurotoxicity and could impair neurogenesis in the hippocampus. The data demonstrated that exosomes secreted from sick cells might damage neurogenesis and promote disease progression in AD.