Nanocrystalline copper substituted nickel zinc ferrites with composition, Ni0.5CuxZn0.5-xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by sol-gel auto combustion technique. All the precursors sintered at 400 oC for 4 h. The stoichiometry and single phase cubic spinel structure confirmed from EDAX and XRD patterns, respectively. Morphology studied by SEM technique. Infrared spectrum of prepared samples investigated at room temperature in the range of 800-300 cm-1. Three major IR absorption bands of tetrahedral frequency in the range of 578-551 cm-1, octahedral frequency in the range of 422-406 cm-1 and ν3 in the range of 352.08 to 325.01 cm-1 observed. The stiffness constant (C11 and C12), elastic moduli, such as Young′s modulus, rigidity modulus, Poisson′s ratio and Debye temperature were determined from IR and structural data. The stiffness constant (C11 and C12) and elastic moduli decreases while Debye temperature increases with copper substitution