Sb2O5 were selected to substitute(Nb0.8Ta0.2)(2)O-5 and the effects of Sb substitution on the dielectric properties of Ag(Nb0.8Ta0.2)O-3 ceramics were studied. The perovskite Ag(Nb0.8Ta0.2)(1-x)SbxO3 ceramics showed no obvious change with x value being no more than 0.08, and the pseudoperovskite unit cell parameters a = c, b and monoclinic angle 0 decrease with Sb concentration increasing. The dielectric properties of Ag(Nb0.8Ta0.2)(1-x)SbxO3 ceramics were found to be affected greatly by the substitution of Sb for Nb/Ta. The E value of Ag(Nb0.8Ta0.2)(1-x)SbxO3 ceramics sintered at their densified temperature increased from 480 to 825 with x from 0 to 0.08, the tan 6 value decreased sharply from 0.0065 to 0.0023 (at 1 MHz) with x increasing from 0 to 0.04, and then kept a stable lower tan 6 value similar to 0.0024 with x to 0.08. The temperature coefficient of capacitance values continuously decreased from a positive value of 1450 ppm/degrees C for x = 0 to a negative value of 38.52 ppm/degrees C for x = 0.08.