Several promising tau imaging probes have been developed by Tohoku University ([18F]THK series), National Institute of Radiological Sciences([11C]PBB3), Eli Lilly ([18F]T807), and Hoffman-La Roche ([18F]R06958948). In this paper we discussed some of the criteria required for the tau imaging probe in Alzheimer's disease. It will be certain that tau imaging plays an important role in an accurate diagnosis and as companion diagnostics.