Samarium doped Mn-Zn ferrite nanoparticles of composition Mn0.5Zn0.5SmxFe2-xO4 (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques to reveal their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter, lattice strain induced increases with the increase in Sm3+ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm3+ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced from EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetic nature of for x = 0, 0.1 the samples. The saturation magnetization is 23.95 emu/g for Mn0.5Zn0.5Fe2O4 sample and increases with rise in Sm3+ ions content. The results are adequately explained and correlated among the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.