The nanocrystalline Co_1-xMn_xFe₂O₄(0≤x≤0.5) ferrites are synthesized by auto-combustion method. The structural properties and phase identification of the samples are studied using X-ray powder diffraction and the Rietveld analysis. The refinement results confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice is partially inverse. The magnetic properties of the prepared samples are studied by using an MeH hysteresis curves. The maximum saturation magnetization and coercivity of samples are 68.94 emu/gm and 1.59 KOe respectively. From ⁵⁷Fe Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Mn²⁺ substitution have been studied. The composition dependent cationdistribution estimated from Rietveld analysis and magnetic studies is in good agreement with each other.