Ln 2 O 2 Te compounds are known to crystallize with two structure types, called A and B, resp. Compounds of the A type crystallize tetragonal in space group I4/mmm with an anti-ThCr 2 Si 2 analogous structure [1]. The B type is thought to crystallize as a superstructure of a yet only known substructure, described in the orthorhombic space group Cmc2 1 [2]. Green platelet like crystals of La 2 O 2 Te 1Ϫx- Se x and Sm 2 O 2 Te 1-x Se x occur as side products during the synthesis of LnSeTe 2 [3] in a LiCl/RbCl flux if the reaction temperature exceeds 800°C. EDX-analyses of the green crystals confirmed the presence of all four elements in both cases. Precession photographs gave Laue class 4/mmm and smaller lattice parameters than those obtained for pure A-La 2 O 2 Te and A-Sm 2 O 2 Te, respectively, suggesting a partial substitution of tellurium by selenium in the structure. The title compounds are the first quaternary mixed chalcogenides of the lanthanides adopting the A type structure. The structure of La 2 O 2 Te 0.77 Se 0.23 (space group I4/mmm, lattice parameters a ϭ 4.092(1) A ˚, c ϭ 12.997(1) A ˚and Z ϭ 2, wR 2 ϭ 0,049) is depicted in the figure.