Single crystals of the composition BaNb0.9S3 have been synthesized from the BaS, Nb, and S mixture and the BaCl2 flux at 900°C. The BaNb0.9S3 structure was refined by X-ray single-crystal and electron diffraction data. The compound is crystallized in the sp. gr. P63/mmc (z = 2) with the unit-cell parameters a = 6.839(1) Å and c = 5.745(1) Å. It was established that the cationic vacancies in the niobium positions are statistically distributed over the structure.