There are two forms, yellow-red α-TeO3 and grey, rhombohedral, β-TeO3 which is less reactive.

[1] α-TeO3 has a structure similar to FeF3 with octahedral TeO6 units that share all vertices.

[2] α-TeO3 can be prepared by heating orthotelluric acid, Te(OH)6, at over 300 °C.

[1] The β-TeO3 form can be prepared by heating α-TeO3 in a sealed tube with O2 and H2SO4.

α-TeO3 is unreactive to water but is a powerful oxidising agent when heated.