The new niobium oxychloride cluster compound, Cs2Ti4Nb6Cl18O6, was obtained by solid-state synthesis techniques in the course of our systematic investigation of metal oxychloride systems aimed at the preparation of low-dimensional cluster compounds. Cs2Ti4Nb6Cl18O6 crystallizes in the trigonal system, with unit cell parameters a = 11.1903(7), c = 15.600(2) Angstrom, space group P (3) over bar 1c, Z = 2. Its crystal structure was determined by single-crystal X-ray diffraction techniques. The full-matrix least-squares refinement against F-2 converged to R-1 = 0.048 (F-o > 4 sigma (F-o)), wR(2) = 0.069 (all data). The structure is based on an octahedral cluster unit ((Nb6Cl6O6i)-O-i)Cl-6(a) in which the six edge-bridging oxide ligands are arranged in two sets of three on opposite sides of the Nb-6 octahedron. Ti3+ ions link the clusters through O-i and Cl-a ligands to form linear chains running along the c axis. The location of titanium ions correlates with the arrangement of oxide ligands around the Nb-6 metal core. The chains interact with each other through additional Ti3+ and Cs+ ions. Interchain interactions are significantly weaker than intrachain interactions, resulting in a quasi-one-dimensional character of the overall structure.