In an aging society, the number of people with dementia has increased. Since Alzheimer's disease and a part of frontotemporal lober degeneration (FTLD-tau) have abnormal tau pathology in brain, these are called Tauopathy. Previously results showed that occurrence of abnormal tau has been involved in development of cognitive dysfunction and neuronal loss indicating that tau-focused drug (inhibitors of tau hyperphosphorylation, tau aggregation and so on) may be valuable in therapy for Tauopathy. This study collated data of clinical trials that evaluated tau-based drugs to help development of agent for dementia drugs in future. We discovered a novel tau aggregation inhibitor, and elucidated the inhibitory mechanism of the compound on tau aggregation. These results suggest that tau aggregation is an important target for therapy of dementia.