This work focused on the processing of low oxygen partial pressure (low-pO2) calcination and sintering with respect to NaNbO3 (NN) of one key member in ferroelectric (Na,K)NbO3. The high-density NN ceramics were successfully prepared without any sintering additives using the low-pO2 process. Comparing conventional air process, the low-pO2 calcined NN powders showed lower defect concentration and higher densification. The low-pO2 sintered NN ceramics had dielectric constant and dielectric loss performance at high temperatures. Furthermore, the low-pO2 sintered NN ceramics indicated ferroelectric behavior, and both maximum polarization and strain improved to two to three times that of conventional air-sintered NN ceramics. From this relatively simple compound, NN, the advantage of low-pO2 is unambiguously demonstrated and points to its consideration. It is hypotheses as a kinetically controlled process that limits the volatility under low-pO2 condition.