The effect of pressure on the vibrational properties of bulk and nanocrystalline powders of cubic bixbyite-type In₂O₃ has been investigated at room temperature by means of Raman spectroscopy up to 31.6 and 30 GPa, respectively. We have been able to follow the pressure dependence of up to sixteen and seven Raman modes in bulk and nanocrystalline cubic In₂O₃, respectively. The experimental frequencies and pressure coefficients of the Raman-active modes of bulk cubic In₂O₃ at ambient pressure are in good agreement with those predicted by our theoretical ab initio calculations. Furthermore, a comparison of our experimental data with our calculations for the Raman modes in rhombohedral corundum and orthorhombic Rh₂O₃-II structures and with already reported Raman modes of rhombohedral corundum-type In₂O₃ at room pressure indicate that Raman scattering measurements provide no experimental evidence of the cubic to rhombohedral or cubic to orthorhombic phase transitions either in bulk material or in nanocrystals up to 30 GPa.