Abstract The crystal structure of the quaternary compound CuTaInSe 3 belonging to the system (CuInSe 2 ) 1‐x (TaSe) x with x= 0.5, was analyzed using X‐ray powder diffraction data. This material is isostructural with the CuFeInSe 3 compound, and crystallize in the tetragonal space group P42c (Nº 112), Z = 1, with unit cell parameters a = 5.7831(1) Å, c = 11.6227(4) Å, V = 388.71(2) Å 3 . The Rietveld refinement of 18 instrumental and structural variables led to R p = 8.0%, R wp = 9.5%, R exp = 6.3% and χ 2 = 1.5 for 4501 step intensities and 144 independent reflections. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)