Dielectric constant (epsilon) of Sn+4/Nb+5 doped Mn-Zn ferrites has been measured as a function of dopant concentration, frequency and temperature. At intermediate concentrations of dopant, an unusual behaviour of dielectric dispersion has been observed due to the occurence of dimensional resonance and thus the interesting results are obtained in the study of variation of epsilon with frequency. For these specimens, in addition to the usual dispersion of epsilon, an increase of epsilon with frequency is observed at two regions in the plot of log epsilon versus log f in support of occurence of dimensional resonance and ferromagnetic resonance behaviour. Studies of dielectric constant and dielectric loss with the variation of temperature have also been carried out to know the above said behaviour beyond magnetic Curie temperature. Results are explained on the basis of correlation between conductivity and dielectric constant, space charge polarisation, grain structure and additional phase formation.