Dielectric and insulating properties of x(Na0.5K0.5)NbO3–(1 − x)BaTiO3 (NKN-BT) with an NKN content between 0.00 ≤ x ≤ 0.10 have been investigated through structural and carrier transfer analysis. Within the specimens that have less than x = 0.10 in the second phase, improved electrical properties were manifested through the increasing NKN content, and microstructural homogenization and refinement of grain size were observed. The dielectric constant was about 94 % higher in the specimen with x = 0.06, and the insulation resistance had a maximum as 1.896 × 1012 Ω in the specimen with x = 0.08. It is proposed that an oxygen vacancy generated at the A-site and leading the degradation of insulation resistance decreased, due to the compensation for the conduction electron generated at the B-site. Also, according to the NKN content, lattice parameter changed with decreasing the tetragonality (c/a). Through the data of Ti K-edge extended X-ray absorption fine structure, the distortion of the crystal structure was revealed and local strain and TiO6 octahedra distortion by off-center displacement of Ti4+ accompanied this finding, due to the substitution of aliovalent cations in the lattice. These decreased the mobility of oxygen vacancies, which led to improved temperature stability and insulation resistance.