Dense, single-phased K-beta"-alumina polycrystals have been prepared from Al-oxyhydroxides by a direct sintering route. The samples were hot-pressed at temperatures between 1300-1500 degrees C. All samples showed a very homogeneous microstructure without exaggerated grain growth. The sample sintered at 1300 degrees C had a single phased beta"-alumina structure, whereas the 1500 degrees C sample consists of a beta/beta"-alumina mixture. The activation energies of all samples were about 0.4 eV, the ionic conductivities at 300 degrees C, obtained by ac-impedance measurements, layed between 10(-3)-10(-4) S/cm. The similarity of the activation energies imply, that the conductivity of all samples is mainly restricted by grain boundary resistivities.