The electronic stopping cross section (SCS) of Al₂O₃ for proton beams is studied both experimentally and theoretically. The measurements are made for proton energies from 40 keV up to 1 MeV, which cover the maximum stopping region, using two experimental methods, the transmission technique at low energies (~40–175 keV) and the Rutherford backscattering at high energies (≈190–1000 keV). These new data reveal an increment of 16% in the SCS around the maximum stopping with respect to older measurements. The theoretical study includes electronic stopping power calculations based on the dielectric formalism and on the transport cross section (TCS) model to describe the electron excitations of Al₂O₃. The non-linear TCS calculations of the SCS for valence electrons together with the generalized oscillator strengths (GOS) model for the core electrons compare well with the experimental data in the whole range of energies considered.