La2–xSrxNiMn1–xSbxO6 (x = 0, 0.08, 0.3) ceramics were prepared by a gel combustion method. Structural, dielectric, and dielectric tunable properties were systematically investigated. A phase transition from mixed monoclinic and rhombohedral phases to monoclinic phase occurs as Sr and Sb contents increase. Impedance and frequency dependence of dielectric constant have been employed to examine the extrinsic contribution to the dielectric properties. Results reveal that the electrode effect has an important influence on the giant dielectric permittivity and dielectric tunability around room temperature.