Background <p>Aqueous route of sol–gel method was used to synthesize nanocrystalline nickel ferrite (NiFe₂O₄) from a stoichiometric mixture of nickel nitrate hexahydtrate and ferric nitrate nonahydrate precursors using aqueous ethanol as solvent and polypropylene glycol as a stabilizing agent. The gel obtained was calcined at various temperatures ranging from 500 °C to 900 °C. The effect of calcination temperature on structural and magnetic properties of nickel ferrite was determined by X–ray diffraction, infrared spectroscopy, thermogravimetry, field emission scanning electron microscopy and vibrating sample magnetometry.</p> Results <p>The results showed a single phase nickel ferrite with a cubic spinel structure having particles of irregular shape and different sizes ranging from 10 to 20 nanometers, randomly distributed to form aggregates.</p> Conclusions <p>The results revealed that the use of polypropylene glycol as a stabilizing agent significantly reduced the agglomeration of nickel ferrite nanoparticles. However, loosely aggregated grains were obtained that got separated with the rise in calcination temperature leading to the formation of more prominent and well–dispersed structures at 900 ºC. Moreover, the samples exhibited high coercivity indispensible for the application of nanoparticles in storage and magnetic devices.</p>