The hydrothermal process was employed to produce single-phase submicrometric NiZn ferrites. The materials were sintered in air at different temperatures and times (1100 to 1400 degrees C, 5 to 240 min). After sintering, highly dense ceramic bodies with different microstructures were obtained. X-ray diffraction, helium pycnometry, nitrogen adsorption technique, and optical and scanning electron microscopy were used to determine the microstructural parameters of the samples. The modeling of the sintering process demonstrates a crossover between the densification mechanisms from grain boundary diffusion to lattice diffusion with increasing sintering temperature. It is also shown that, in the final-stage sintering, the grain growth kinetics is controlled by pore drag.