Ultrafine Mn(II)-ferrites represented by MnxFe3-xO4 (x = 0.19-0.84) were synthesized by hydrolysis of Mn2+, Fe2+, and Fe3+ ions, followed by aging of the coprecipitate at 60 degrees C without any hydrothermal and heat treatments. Nearly spherical and uniform particles were formed, the average crystallite size of which ranged from 8 to 13 nm. The Mn2+ substitution of the ultrafine ferrite was corroborated by a linear increase in the lattice constant with an increase in the Mn(II) content of the products. The Mossbauer spectra revealed that the superparamagnetic fraction was small in the samples at room temperature, and the ultrafine particles were almost ferrimagnetic. In the absence of Fe2+, the coprecipitation of Mn2+ and Fe3+ (the Mn(II)/Fe-total mole ratio = 0.5) resulted in an amorphous compound, indicating that the Fe2+ ions facilitate the formation of the spinel ferrite during neutralization of the metal ions. This effect of Fe(II) ions on the ferrite formation can be attributed to the formation of dark red complex cation composed of Fe(II), Fe(III) and Mn(II) as the intermediate into ferrite. The magnetic properties of the ultrafine ferrites at room temperature were also given.