Three different uranium trichloride hydrates of the formulas UCl 3 ·2H 2 O·2CH 3 CN, UCl 3 ·6H 2 O and UCl 3 ·7H 2 O have been isolated from methylcyanide solutions of UCl 4 , with a 1–5% water content, by reduction with liquid zinc amalgam. The crystal and molecular structures of the hydrates have been determined by X-ray single crystal analysis. UCl 3 ·2H 2 O·2CH 3 CN crystallizes in the triclinic system (space group P1¯) forming infinite zigzag chains in the [010] direction. The coordination polyhedron of the uranium atom is a bicapped trigonal prism, formed by two oxygen atoms of the water molecules, four bridging chlorine atoms, one terminal chlorine atom and one nitrogen atom of the methylcyanide molecule. UCl 3 ·6H 2 O crystallizes in the monoclinic system (space group P2/n), with a monomeric structure. The uranium ion is eight-coordinated by two chlorine atoms and six oxygen atoms of the water molecules, which form a distorted square antiprism. UCl 3 ·7H 2 O crystallizes in the triclinic system in the space group P1¯. The characteristic feature of this structure are [(H 2 O) 7 UCl 2 U(H 2 O) 7 ] 4+ dimers. The coordination polyhedra, in the form of a tricapped trigonal prism, are linked through the complex network of the hydrogen bonds. UCl 3 ·6H 2 O and UCl 3 ·7H 2 O are isostructural with their lanthanide analogues.