Nanoparticles of MnxZn1-xFe2O4 (0 ≤ x ≤ 1.0) compositions were synthesized via sol-gel process. The structure, thermal stability and magnetic properties of as-prepared and annealed samples have been investigated. Although, as-prepared and 1200 °C air annealed samples exhibit cubic spinel ferrite phase, they decompose into α-Fe2O3, or/and α-Mn2O3 phases along with the poor quality of ferrite phase on annealing at 600 °C in air. Present investigations show that the stability of spinel ferrite phase is sensitive to (i) Mn concentration (ii) the annealing temperature and (iii) environments (air, Oxygen and Argon atmosphere) in which annealing experiments were carried out. A comparative study of structural and magnetic properties of Argon and air annealed samples suggest that differential oxygen partial pressure plays a significant role in stability as well as magnetic properties. Therefore, we suggest the deterioration of magnetic properties in Mn-Zn ferrite nanoparticles is due to depletion of Fe3+ ions from spinel structure that affects the cation distribution. It is also shown that magnetic properties can be tuned by controlling the process conditions. From these studies we propose a phenomenological model which explains the observation of present study. © 2018 Elsevier B.V.