Promethium(III) sulfide is a binary inorganic compound with the chemical formula .
Promethium(III) sulfide can be produced by treating metallic promethium with sulfur:
Once prepared, promethium(III) sulfide can be purified by chemical vapor transport using iodine.
Promethium(III) sulfide can also be prepared by treating the sulfate with hydrogen sulfide at elevated temperatures:
The compound forms garnet red crystals of the orthorhombic system, space group I3d and exists in ñ and ò forms.