Violet crystals of AsPh4[W(O)Cl3(HN3S2)] were obtained by partial hydrolysis of AsPh4[WCl4(N3S2)] in a saturated solution in CH2Cl2/CCl4. Its IR spectrum is reported. The crystal structure was determined by X-ray diffraction (2284 independent observed reflexions, R = 0.041). Crystal data: triclinic, space group P1̄, Z = 2, a = 812.2, b = 1268.4, c = 1343.9 pm, α = 88.58, β = 82.04 and γ = 88.26°. The compound consists of AsPh4⊕ cations and [W(O)Cl3(HN3S2)⊖ anions in which the tungsten atoms have a distorted octahedral coordination with one oxo-ligand (171 pm), three chlorine atoms and two nitrogen atoms of the planar (HN3S7)2⊖ ligand. The WN bond lengths are 183 and 226 pm; the longer WN bond is due to the hydrogen atom attached to its N atom and to the trans influence of the oxo group. The crystal packing corresponds to one of the types frequently found among tetraphenylphosphonium compounds with cations stacked to parallel columns.