The purpose of this research is to examine the change with Al3+ contribution in structural, magnetic, and electrical properties of Mg0.75Zn0.25AlxFe2-xO4 (x=0, 0.2, 0.4) ferrites fabricated by co-precipitation technique. The characteristics of samples are investigated using XRD, SEM, FTIR, VSM, and impedance spectroscopy. XRD characterization confirmed that the samples were in cubic spinel structure with Fd/3 m space group. The crystallite size was concluded from broadening the diffraction peaks using the Debye-Scherrer's (D-s) and Williamson-Hall (DW-H) method. The crystal sizes D-s (from 24.22 to 36.94 nm) and DW-H (from 19.01 to 28.99 nm) of the Mg-Zn ferrites samples increased with Al3+ contribution. FTIR spectra show the presence of characteristic absorption bands of ferrites named as nu(1) and nu(2), one in the range of 550-577 and the other in the range of 475-478. The M-H hysteresis loops of all samples in the range of +/- 60 kOe showed the superparamagnetic behavior with small M-r and H-c values. The H-c increased from 128.3 to 265.1Oe while the M-s decreased from 7.34 to 4.43 emu/g with increasing of the Al3+ substitution. The changes in dielectric properties such as AC conductivity (sigma(AC)) dielectric constant (epsilon', epsilon ''), loss factor (tan theta), impedance (Z' ,Z '') and modulus (M', M '') of samples were investigated. Imaginary dielectric constant (epsilon '') increase from 713 to 4.4 x 10(6) with rising of the Al3+ substitution at 20 Hz. Finally, according to the Nyquist graphs drawn using the modulus values, it has been shown that the materials are compatible with the Debye model.