Room temperature Mössbauer, X-ray and IR spectral studies were carried out for the spinel system Mn0.5Zn0.5AlxFe$_{2-x}$O4, $0 \le x \le 1$, prepared using the usual ceramic technique. X-ray patterns confirm that all samples have single phase cubic spinel structure. The Mössbauer spectra of the samples show a six-line magnetic pattern and a central paramagnetic phase. They are assigned to two magnetic subpatterns and two quadrupole doublets due to Fe3+ ions at the tetrahedral A-sites and octahedral B-sites. The effect of increasing the Al3+ content x on the hyperfine interaction parameters is studied and discussed. The lattice constant, oxygen positional parameter, mean ionic radius of the A- and B-sites, bond lengths, edges and interionic distance are affected by the additional process x. They are determined and discussed as functions of x. The IR spectra shows six absorption bands in the range 222–1033 cm−1. The bands are attributed to the corresponding metal-oxygen complexes in the A- and B-sites. The hyperfine interaction parameters, the IR band positions and intensities reveal their dependence on the Fe3+−O2− bond length and the interionic distance at A- and B-sites. The variation of the quadrupole doublet splitting for the B-site and the oxygen parameter reveal the increasing trigonal distortion of the B-site oxygen coordination. The IR absorption at 222 cm−1, the velocity of the infrared waves when passed through the samples and the jump rate of the lattice vacancies were found to decrease.