Neuropsychiatric diseases are major diseases with high prevalence in recent years. These diseases usually cause cognitive impairments of neuropsychiatric patients and threat to their health and life. However, we still lack of objective standard for clinically diagnosis so far, and cannot fully rely on traditional treatments of medicine because of their side effects. Thus, it becomes essential to develop effective and objective methods for diagnosis and treatment. EEG can reflect our brain’s real-time state, that could be used as an indicator of brain impairment by detecting the characteristic rhythms. Gamma rhythms (~25-100 Hz) play an important role in the higher-level functions of brain, especially associated with cognition and memory. Importantly, disrupted gamma rhythms have been found in neuropsychiatric diseases of both clinical patients and animal models, which suggests novel diagnostics based on gamma rhythms measurements in core brain regions of cognition. In this paper, we reviewed the recent studies on impaired gamma rhythms in neuropsychiatric diseases, including some major neurodegenerative and psychiatric diseases. We focused on the characteristics of gamma rhythms in regulating cognition, learning and memory in human and rodents, and analyzed the underlying neural mechanisms in cellular and molecular levels. Therefore, these findings may shed light to highly effective diagnosis of neuropsychiatric diseases in future by targeting gamma rhythms detection in EEG signals.