We report the phase stability, microstructure and magnetic properties of MgFe₂O₄ nanoparticles under different annealing conditions. Magnetic properties of MgFe₂O₄ are strongly influenced by the crystal structure and
morphology, which in turn, depend on annealing conditions. The as-prepared and samples annealed at 1200 °C show a pure spinel phase. Whereas the samples annealed and quenched at 600 °C-1000 °C exhibit the spinel phase along with a small fraction of the secondary phase of α-Fe₂O₃, which causes deterioration of magnetic properties. On the other hand, samples annealed at 600 °C-1000 °C under Argon atmosphere display superior magnetic properties (M = 44-56 emu/g at room temperature) due to the presence of pure spinel phase. Interestingly, the sample quenched at 1200 °C exhibits large saturation magnetization, MS = 63 emu/g at 5 K which is arising from the optimum cationic distribution (δ = 0.77) grown at elevated temperature is retained in the rapid cooling process.