The crystal structure of the La1-xKxCo1-xNbxO3 system showed a transition from a rhombohedral to a cubic structure, and then to an orthorhombic structure as the amount of KNbO3 was increased. Dielectric measurements were carried out as a function of temperature (253-473 K) and frequency (100-100 kHz). The value of the dielectric constant was about 58,000 at room temperature, with a low dissipation factor (D=0.4) from the sample with x=0.1 sintered at 1673 K for 2 h and measured at 100 Hz. The frequency of the dielectric relaxation for the sample of x=0.1 in the temperature range from 253 to 473 K was observed. The activation energy of the dielectric relaxation is estimated to be 0.061 eV and the lattice vibrational phonon frequency tau(0) is 1.881x10(-3) s. (c) 2007 The Electrochemical Society.