Manganese ferrite nanocrystals were prepared from an aqueous solution containing metal nitrates and various of concentrations of poly(vinyl pyrrolidone) as a capping agent to stabilize the particles and prevent them from agglomerating. To stabilize the particles, they were thermally treated at 873 K as an optimum calcination temperature. The presence of the crystalline phase in each sample was confirmed by X-ray diffraction (XRD) analysis that showed that the presence of the PVP increased the degree of crystallinity of the nanoparticles that were formed. The average particle size and the morphology of the manganese ferrite nanoparticles were determined by transmission electron microscopy (TEM), and these parameters were found to differ with the various concentrations of PVP. Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of metal oxide bands for all of the PVP concentrations and confirmed the absence of organic bands for PVP concentrations less than 0.055 gm/ml.