Osmium(III) chloride is an inorganic chemical compound of osmium metal and chlorine with the chemical formula OsCl3.

[1][2] Osmium(III) chloride can be made by a reaction of chlorine with osmium: It can also be made by heating of osmium(IV) chloride: Osmium(III) chloride forms black-brown crystals.

[3] Osmium(III) chloride forms a hydrate of the composition OsCl3·3H2O with dark green crystals.

[4] Osmium(III) chloride hydrate is used as a precursor material for the production of dichlorodihydridoosmium complex compounds and other compounds.

[5] It is the precursor to a variety of arene complexes.