Rubidium triiodide is an inorganic compound with the chemical formula RbI<sub>3</sub>. It is composed of Rb<sup>+</sup> and .
Rubidium triiodide can be obtained by heating rubidium iodide and iodine in aqueous solution:
Rubidium triiodide is an orthorhombic black crystal, isomorphic to caesium triiodide, with space group Pnma, unit cell parameters a = 1090.8 pm, b = 665.5 pm, c = 971.1 pm. Upon heating to 270 ðC, the rubidium triiodide decomposes into rubidium iodide and elemental iodine. It is soluble in ethanol and decomposes in ether.
It has long been believed that rubidium triiodide reacts further with iodine to form RbI<sub>7</sub> and RbI<sub>9</sub>, but this has been refuted by recent studies.