Amyloid-β (Aβ) oligomers are recognized as the primary neurotoxic agents in Alzheimer’s disease (AD). Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline in AD. NMN restored levels of NAD+ and ATP, eliminated the accumulation of reactive oxygen species (ROS) in the Aβ oligomer-treated hippocampal slices. The present study indicates that NMN could restore cognition in AD model rats. The beneficial effect of NMN is produced by ameliorating neuron survival, improving energy metabolism and reducing ROS accumulation.