The basic properties of ceramic materials depend very much on heir bulk properties. With ceramics, and other similar materials the crystal-lattice continuum that defines the intrinsic properties is interrupted by grain boundaries, and this strongly influences the extrinsic properties. The distribution, the extent and the structure of the grain boundaries represent a major unavoidable perturbation to the bulk properties, and in principle, these perturbances define the ceramics status. Various microstructure models for MnZn-ferrites were developed that more-or-less satisfactorily explain their properties and can help in designing improvements. However only recent developments in analytical methods and TEM analyses make it possible to investigate the grain boundaries on the nano-scale. The grain boundaries are of key importance during the microstructure development and the functioning of electronic ceramics. In MnZn-ferrite ceramics-the diversity of the grain boundary function is particularly obvious. The grain-boundary mobility during sintering and grain growth must be adapted to the desired microstructure, and the resistance must be as high as possible in order to decrease the eddy current loss. In order to improve the properties of the modern electronic ceramics, the studying and understanding of grain boundaries on the nano-scale is important. Here, some recent studies of the grain-boundary on the nano-scale in MnZn-ferrite are reported.