Rhenium(III) bromide is a chemical compound with the formula Re3Br9.

This compound reacts with water to form rhenium(IV) oxide and is isostructural with rhenium(III) chloride.

[1][4] This compound is prepared by the reaction of rhenium metal and bromine gas at 500 °C under nitrogen:[2] If there is oxygen in the atmosphere, it will instead form rhenium(III) oxybromide.

[2] However, the most common method of producing this compound is by first reacting potassium hexabromorhenate(IV) with silver nitrate, which forms silver hexabromorhenite(IV), then this compound is heated to 600 °C to form rhenium(III) bromide.

[1][3] An alternative method is a thermal decomposition of rhenium(V) bromide.