The first cerium iodothiosilicate, Ce₃(SiS₄)₂I, has been synthesized from the reaction of cerium sulfide with silicon, iodine and sulfur at high temperature. This compound crystallizes in the monoclinic symmetry (space group C2/c and Z=4) with the powder refined cell parameters: a=15.9634(5), b=7.8502(2), c=10.8664(3) Å, β=97.931(2)°. The crystal structure was refined to R(%)=2.17 and R_w(%)=2.60 from single crystal X-ray diffraction data. Ce₃(SiS₄)₂I presents tunnels in which are located the iodide anions surrounded by three ceriums, in [ICe₃ ] isosceles triangular entities. The tunnels are constituted of a three dimensional network made of (CeIS₈) polyhedra (trigonal prisms of sulfur tricapped by two sulfur and one iodine atom) linked to (SiS₄) tetrahedra. Magnetic susceptibility measurements and UV–VIS diffuse reflectance spectroscopy are consistent with the occurrence of Ce^III ions, whereas band structure calculations indicate that the phase is a semiconductor. The charge balance in the material can be written as : Ce^III₃Si^IV₂I^–IS^–II₈ .