(1-x)(K0.5Na0.5)NbO3-xBa(2)NaNb(5)O(15) [(1-x)KNN-xBNN, 0x0.1] ceramics were prepared by solid-state reaction method. X-ray diffraction analysis of the ceramics revealed that the crystal structure changed from orthorhombic to rhombohedral with increasing BNN content. Dielectric measurement showed that the ceramics exhibited good dielectric temperature stability over a wide temperature range. Basic mechanisms of the conduction and relaxation processes have been investigated using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated and oxygen vacancies were the possible ionic charge carriers at higher temperatures.