Microstructural evolution and microwave dielectric properties of liquid-phase-sintered 0.9MgTiO(3)-0.1CaTiO(3) dielectric ceramic material have been investigated as a function of oxygen partial pressure p(O2)) during sintering. Sintering in a weakly reducing atmosphere (p(O2) = 10(-14) atm) generally increased the density, permittivity, quality factor (Q x f), and the temperature coefficient of resonance frequency (tau(f)), but further reducing atmosphere down to p(O2) of 10(-14) atm generally decreased Q x f and tau(f). When the 5 wt% lithium borosilicate glass-added specimen was sintered at 950 degrees C and p(O2) = 10(-14) atm, it demonstrated a permittivity of 18.8, Q x f of 19 000 GHz, and tau(f) of 10 x 10(-6) K-1.