Li17Sb13S28 was synthesized by solid-state reaction of stoichiometric amounts of anhydrous Li2S and Sb2S3. The crystal structure of Li17Sb13S28 was determined from dark-red single crystals at room temperature. The title compound crystallizes in the monoclinic space group C2/m (no.12) with a=12.765(2)angstrom, b=11.6195(8)angstrom, c=9.2564(9)angstrom, =119.665(6)degrees, V=1193.0(2)angstrom(3), and Z=4 (data at 20 degrees C, lattice constants from powder diffraction). The crystal structure contains one cation site with a mixed occupation by Li and Sb, and one with an antimony split position. Antimony and sulfur form slightly distorted tetragonal bipyramidal [SbS5E] units (E=free electron pair). Six of these units are arranged around a vacancy in the anion substructure. The lone electron pairs E of the antimony(III) cations are arranged around these vacancies. Thus, a variant of the rock salt structure type with ordered vacancies in the anionic substructure results. Impedance spectroscopic measurements of Li17Sb13S28 show a specific conductivity of 2.9x10(-9-1)cm(-1) at 323K and of 7.9x10(-6-1)cm(-1) at 563K, the corresponding activation energy is E-A=0.4eV below 403K and E-A=0.6eV above. Raman spectra are dominated by the SbS stretching modes of the [SbS5] units at 315 and 341cm(-1) at room temperature. Differential thermal analysis (DTA) measurements of Li17Sb13S28 indicate peritectic melting at 854K.