A series of samples in the system Ni0.65Zn0.35CuxFe2−xO4 (x=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by the usual ceramic technique. X-ray analysis showed that they were cubic spinel (single phase). Young's modulus, the dielectric loss and the change in capacitance under mechanical stress were measured for the samples. Young's modulus decreased with increasing Cu content. This is due to the fact that Cu2+ ions entered the lattice substitutionally for Fe3+ ions at the octahedral sites, creating lattice vacancies gave rise to lattice strain.