The preparation of manganese ferrite thin films by the reactive evaporation of oxidic materials is reported. The process is not critical and provides homogeneous mirror-like films with spinel structure. An annealing procedure below 750 °C has a strong influence on the properties of the films. Special attention is paid to the partial oxygen pressure during the annealing process. For this purpose data are collected from the literature concerning the equilibrium conditions of the spinel structure for varying manganese-iron contents. The lattice constant of the spinel structure of the films is determined by electron diffraction.