Significance Knowledge of the structure of MgSiO ₃ melt at pressures near the Earth’s core–mantle boundary is important in understanding geochemical and geophysical processes at the region. However, there is no structural determination under such ultrahigh pressures. A double-stage Paris–Edinburgh press combined with multiangle energy dispersive X-ray diffraction enabled in situ structure measurements on MgSiO ₃ glass up to 111 GPa. We report direct experimental evidence of a structural change in this glass at pressures greater than 88 GPa, which is shallower than the pressure of the Earth’s core–mantle boundary. Considering similarities in pressure-induced structural changes between silicate melts and glasses, a similar ultrahigh-pressure structural change may occur in MgSiO ₃ melts in the deep lower mantle.