It is critically important to control grain boundaries in ceramics. In classical sense of grain boundary engineering, the choice of sintering aid, grain boundary wetting by liquid phase, grain boundary crystallization etc. are the key technologies to fabricate commercial ceramics, and such basic techniques to control grain boundary phases are still common in tailoring engineering and functional ceramics. However, sintering in solid state becomes more important than before, in particular, in high-performance oxide ceramics because high-purity raw powders are available in recent years by the advancement of powder processing techniques. In such modem ceramics, various properties are very sensitive to a small doping of cation, which segregates in grain boundaries. To understand the small dopant effect, we need a knowledge of the change in local bonding state in grain boundaries with segregation. In this paper, our several trials to control grain boundary structure and chemistry ceramics in modem high-performance oxide will briefly be introduced.