Abstract The crystal structure of the chalcogenide compounds CuFeAlSe 3 and CuFeGaSe 3 , belonging to the system I‐II‐III‐III 3 , were characterized using X‐ray powder diffraction data. Both compounds crystallize in the tetragonal space group P42c (N° 112), Z = 1, with unit cell parameters a = 5.609(1) Å, c = 10.963(2) Å for CuFeAlSe 3 and a = 5.6165(3) Å, c = 11.075(1) Å for CuFeGaSe 3 . These compounds are isostructural with CuFeInSe 3 , and have a normal adamantane structure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)