Dependence of initial permeability of Mn-Zn ferrite single crystals on crystallographic orientation was studied theoretically and experimentally. The crystallographic anisotropy of initial permeability of Mn-Zn ferrite single crystals has been believed because of the previous experimental results and magnetocrystalline anisotropy. The permeability of the single crystal was theoretically derived by the use of the magnetocrystalline anisotropy energy on both mechanisms of the domain wall displacement and rotation magnetization, respectively. When the magnetic domain structure in the crystal is formed so that the spontaneous magnetization directs each easy direction at random, it is proved theoretically that there is no crystallograhic dependence of the initial permeability of Mn-Zn ferrite single crystals without stress. This independence was proved by measuring the permeability of Mn-Zn ferrite single crystal specimens having little composition segregation without stress. The permeability spectra and permeability-temperature relation of the crystal specimens was also measured. The crystallographic dependence which has been shown can be considered to be due to the composition segregation and residual stresses of the tested materials.