Nanocrystalline nickel-zinc ferrites were produced by hydrothermal processing. The powders were submitted to a rapid sintering method (fast-firing) in a wide range of temperatures (1100-1450 degreesC), times (5-240 min), and heating/cooling rates (100, 250, and 400 degreesC/min). The results showed that different microstructures are obtained under these fast-firing conditions. Their effects on the microstructural evolution are discussed in terms of a qualitative model, which indicated the relative predominance of the densification and grain growth rates.