MgNb₂O₆-doped (Ba_0.71Sr_0.29)TiO₃((Ba,Sr)TiO₃)-based capacitor ceramics were prepared by solid-state method. The influence of MgNb₂O₆(MNO) doping amount on the dielectric properties, phase composition, and microstructure of (Ba,Sr)TiO₃-based ceramics were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), among other tests. The results showed that the relativity permittivity of (Ba,Sr)TiO₃-based capacitor ceramics decreased; dielectric loss increased, then decreased, and finally increased; the resistivity first decreased, then increased, and finally decreased; and withstand voltage strength (E_b) first decreased firstly, then increased, and finally decreased when MNO doping amount increased. When the doping amount of MNO was 2.0 wt%, the (Ba,Sr)TiO₃ ceramics had a maximum dielectric constant of 1 670 and minimum dielectric loss of 0.005 6. When the doping amount of MNO was 8.0 wt%, (Ba,Sr)TiO₃ ceramics had a maximum resistivity of 65.23×10¹⁰ Ω·cm and maximum withstand voltage strength of 7.7 kV/mm (DC). When the doping amount of MNO was 10.0 wt%, (Ba,Sr)TiO₃ ceramics exhibited less percentage of capacitance variation with temperatures of +0.18% and -28.29%. (Ba,Sr)TiO₃ ceramics doped with MNO had a perovskite structure. The doping of MNO can decrease capacitance variation with temperature.