The real part of the dielectric constant (epsilon') and the dielectric loss angle (tan delta) as well as the ac conductivity of ferrite Mg1+xTixNdyFe2-2x-yO4 0.1 less than or equal to x less than or equal to 0.9 at fixed Nd concentration of 0.025 were measured at different temperatures as a function of frequencies. The variation of activation energy as a function of the applied frequency was reported. The obtained data were discussed on the basis of the valence exchange between (Fe3+, Fe2+), (Fe2+, Nd3+) and (Fe2+, Ti4+). Also the effect of sintering temperature and heating rate of preparation were discussed. (C) 2003 Kluwer Academic Publishers.