Alzheimer's disease (AD) and schizophrenia are two different diseases, but both of them show cognitive dysfunction. Parvalbumin positive neurons (PV positive neurons) are one of inhibitory interneurons, which regulate the excitation / inhibition balance, and participate in the generation of gamma oscillation. They are pivotal for the processing of information, signal integration and output, and are closely related to cognitive functions such as learning and memory, attention, awakening state and social interaction. The regulation of PV positive neurons on cognitive function suggests that they are involved in the pathogenesis of AD and schizophrenia. Therefore, we will review the recent progress on the roles and the mechanisms of PV positive neurons underlying the cognitive dysfunction in AD and schizophrenia, as well as on the treatment of cognitive dysfunction through PV positive neurons.