A single crystal of tetragonally distorted manganese-iron spinel of compositionMn1.85Fe1.15O4has beenstudied by microwave resonance in the temperature range 77–390°K. The anisotropy has tetragonal symmetry,with thecaxis hard and the tetragonalaaxis (corresponding to the [110] direction in the undistortedcubic structure) easy. The data are analyzed in terms of an anisotropy energy of the form:EA = K1&agr;32+K2&agr;34+K3&agr;14+&agr;24,wherein&agr;1and&agr;2are direction cosines of the magnetization referred to the tetragonalaaxes, and&agr;3is thedirection cosine of the magnetization referred to thecaxis. The second-order axial componentK1/Misapproximately 3 kgauss at room temperature and remains relatively constant as the temperature is lowered to160°K, below which it increases rapidly. The quantityK3/M, which measures the anisotropy in the basalplane, is about −25 gauss at room temperature and increases to a few hundred gauss at 77°K. A temperatureindependentgeff = 2.01adequately describes the measurements. Linewidths vary from 250 gauss in thetetragonal [110] direction to 400 gauss in thecdirection at room temperature and increase with decreasingtemperature.