Uranium triiodide is an inorganic compound with the chemical formula UI3.

It is a black solid that is soluble in water.

Uranium triiodide can be obtained from the direct reaction of its constituent elements:[3] When the reaction is conducted in tetrahydrofuran (THF), the product is the blue complex UI3(THF)4.

[4] It crystallizes in the orthorhombic crystal system (plutonium tribromide-type) in the space group Ccmm with the lattice parameters a = 432.8 pm, b = 1401.1 pm, and c = 1000.5 pm and four formula units per unit cell.

[1] Uranium triiodide can be used as a Lewis acid catalyst for various Diels-Alder reactions carried out under mild conditions.