Amorphous indium oxide is insoluble in water but soluble in acids, whereas crystalline indium oxide is insoluble in both water and acids. The crystalline form exist in two phases, the cubic (bixbyite type) and rhombohedral (corundum type). Both phases have a band gap of about 3 eV. The parameters of the cubic phase are listed in the infobox. The rhombohedral phase is produced at high temperatures and pressures or when using non-equilibrium growth methods. It has a space group R3c No. 167, Pearson symbol hR30, a = 0.5487 nm, b = 0.5487 nm, c = 0.57818 nm, Z = 6 and calculated density 7.31 g/cm3.
Thin polycrystalline films of indium oxide doped with Zn are highly conductive (conductivity ~105 S/m) and even superconductive at helium temperatures. The superconducting transition temperature Tc depends on the doping and film structure and is below 3.3 K.
When heated to 700 °C Indium(III) oxide forms In2O, (called indium(I) oxide or indium suboxide), at 2000 °C it decomposes.
It is soluble in acids but not in alkali.
With ammonia at high temperature indium nitride is formed 
In2O3 + 2 NH3 → 2 InN + 3 H2O
With K2O and indium metal the compound K5InO4 containing tetrahedral InO45− ions was prepared.
Reacting with a range of metal trioxides produced perovskites for example:
^Prewitt, Charles T.; Shannon, Robert D.; Rogers, Donald Burl; Sleight, Arthur W. (1969). "C rare earth oxide-corundum transition and crystal chemistry of oxides having the corundum structure". Inorganic Chemistry. 8 (9): 1985–1993. doi:10.1021/ic50079a033.
^Li, C; Zhang, D; Han, S; Liu, X; Tang, T; Lei, B; Liu, Z; Zhou, C (2003). "Synthesis, Electronic Properties, and Applications of Indium Oxide Nanowires". Annals of the New York Academy of Sciences. 1006: 104–21. doi:10.1196/annals.1292.007. PMID14976013.