Ferrites with the general formula Mg1+xMnxFe2-2xO4 (where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared by the standard ceramic technique and studied by means of X-ray diffraction, magnetization, a.c. susceptibility and dielectric constant measurements. The X-ray analysis confirmed the single-phase formation of the samples. The lattice parameter is found to increase up to x = 0.3 and thereafter it decreases as x increases. The cation distribution has been studied by X-ray analysis and magnetization. Magnetization results exhibit collinear ferrimagnetic structure for x < 0.3 and thereafter structure changes into non-collinear for x > 0.3. Curie temperature (T-C) obtained from a.c. susceptibility data decreases with increasing x. The dielectric constant (epsilon'), loss tangent (tan delta) show strong frequency dependence. (C) 2005 Springer Science + Business Media, Inc.