High-energy mechanical activation of the starting oxides was found to reduce dramatically or even suppress the frequency shift of the dielectric permittivity maximum of ceramic ferroelectrics-relaxors PbMg1/3Nb2/3O3 and PbFe1/2Ta1/2O3 sintered from the mixture of these oxides. At the same time, the value of permittivity maximum does not change substantially. On increase of the sintering temperature above approximate to 1100 degrees C for PbFe1/2Ta1/2O3 and approximate to 1200 degrees C for PbMg1/3Nb2/3O3 the effect of mechanical activation on dielectric properties of both these ceramics gradually vanishes.