Mn-Zn ferrite nanoparticles of Mn0.6Zn0.4Fe2O4 composition were synthesized through sol-gel auto combustion process. The phase formation, thermal stability, morphology, and magnetic properties of as-prepared and heat treated samples have been investigated. It is observed that as-prepared spherical particles (10-40 nm) transform into single phase spinal structure of ∼ 500) nm long cylindrical rods of 60 nm diameter, when annealed at 1200 °C in air. Interestingly, when the samples were annealed at 600 °C in air Fe2O3, Mn2O3 impurity phases appear along with poor quality ferrite phase. On the other hand, samples annealed at 600 °C, under inert gas conditions showed well-ordered single phase spinal structure with large Ms=60) emu/g and Hc=55 Oe. Furthermore, it is shown that on rapid cooling, the sample from 1200 °C yields a good quality spinel structure with enhanced soft magnetic properties Ms=62.3) emu/g;Hc= 3 Oe). © 2014 IEEE.