Osmium(III) chloride is an inorganic compound of osmium and chlorine with the chemical formula .
Osmium(III) chloride can be prepared by treating osmium with chlorine:
It can also be prepared by the decomposition of osmium(IV) chloride:
Osmium(III) chloride hydrate is a precursor for the production of dichlorodihydridoosmium complexes and other compounds.
It is the precursor to a variety of arene complexes.