Superparamagnetic single phase zinc ferrite nanoparticles have been prepared by coprecipitation method at 20 °C without any subsequent calcination. The composition, crystallite size, microstructure and magnetic properties of the prepared nanoparticles were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), Fourier transmission infrared spectrum (FTIR) and vibrating sample magnetometer (VSM). The XRD pattern proved that the nanoparticles were single phase cubic spinel ZnFe2O4 with crystallite size of 5nm. The magnetic measurement showed that the as-prepared nanoparticles of zinc ferrite were superparamagnet at room temperature.