Ternary chalcogenides, GeSb2Se3 and Ge3Sb4Se7, were synthesized and characterized. These chalcogenides are the first ternary selenides in a ternary Ge–Sb–Se system that feature a layer structure related to black phosphorus and SnSe-type structures. Both compounds contain a ∞ 1[Sb2Se2]2– unit with Sb+ cations in a zigzag Sb–Sb chain structure, and Sb3+ cations in a distorted NaCl100-type of ∞ 1[Ge n–2Sb2Se n ]2+ unit (n = 4, 5). These materials exhibit n-type semiconducting properties with thermal conductivity significantly lower than that of GeSe and Sb2Se3, which could be correlated to the 1D Sb+ chain and disordered sites with different Ge/Sb compositions. It is anticipated that these newly discovered ternary chalcogenides may provide unique properties with enhanced thermoelectric properties.