The effect of sintering in air and oxygen atmospheres on microstructure and microwave dielectric properties of ZnNb₂O₆ ceramics has been investigated and compared. For most cases samples sintered in oxygen atmosphere exhibited higher density than those sintered in air atmosphere. The highest densities obtained for samples sintered in air and oxygen atmospheres were 93.6 and 95.2% of the theoretical value, respectively. The variation of relative permittivity (ε _r) values with temperature for samples sintered in air and oxygen atmospheres followed the variation in the density values. The highest values of ε _r for samples sintered in air and oxygen atmospheres were 22.6 and 23.5, respectively. A considerable improvement in Q × f (Q and f are quality factor and resonant frequency, respectively) was obtained for most sintering temperatures when sintering was performed in oxygen atmosphere. The highest Q × f obtained for samples sintered in air and oxygen atmospheres were 82,688 and 81,204 GHz, respectively. Temperature coefficient of resonant frequency (τ _f) values closer to the ideal value (0 ppm/°C) was exhibited by samples sintered in oxygen atmosphere. The best values of τ _f for air and oxygen sintering atmospheres are −59.4 and −48.6 ppm/°C, respectively.