The anhydrous compound[2] is a green powdery[2] solid at room temperature.

Heating neodymium and iodine in an inert atmosphere produces this salt:[citation needed] It can also be prepared by the reaction of neodymium(III) oxide and hydroiodic acid to make a hydrate:[4] The anhydrate can then be obtained by heating the nonahydrate with ammonium iodide:[4] Neodymium(III) iodide forms green, water-soluble hygroscopic crystals.

[5] NdI3 also forms some compounds with N2H4, such as NdI3·3N2H4·2H2O which is a dark green crystal, soluble in methanol and ethanol and insoluble in water, benzene and toluene, d20°C = 3.42 g/cm³.

[6] NdI3 also forms some compounds with urea, such as NdI3 5CO(NH2)2 which is a lavender color crystal.

[7] NdI3 also forms some compounds with thiourea, such as NdI3·2CS(NH2)2·9H2O which is a pale pink crystal.