Ba0.6Sr0.4TiO3 powder was synthesized by a citrate method. The powder with a pure pervoskite phase and superfine particle morphology was produced at low calcining temperature of 550°C by controlling heating rate during the calcination. Microstructure and nonlinear dielectric properties of the ceramic specimens were investigated with respect to sintering temperature. It was found that the superfine morphology of the powder effectively reduced the sintering temperature of the ceramic specimens. The ceramic specimen sintered at 1260 °C attained about 95% of the theoretical density. At room temperature, the ceramic specimen showed a dielectric constant of 3010 and a dielectric loss of 0.48% at 10 kHz together with a tunability of 32.4% at 10 kHz and 20 kV/cm.