We report the syntheses of single crystals and polycrystalline phase of a new quaternary sulfide, Ba3.14(4)Sn0.61(1)Bi2.39(1)S8, by the high-temperature sealed tube method. A single-crystal X-ray diffraction study established that the title compound is non-stoichiometric and crystallizes in the orthorhombic D2h16-Pnma space group with cell parameters of a ​= ​12.4479(7) Å, b ​= ​4.3140(2) Å, c ​= ​28.7860(17) Å, and Z ​= ​4. The crystal structure is composed of infinite chains of ∞1[Sn(1)0.61Bi(1)0.39S3]2.39− and ∞1[Bi(2)Bi(3)S5]4− stripes, which are separated by Ba2+ cations. The optical absorption study of the polycrystalline Ba3.2Sn0.6Bi2.4S8 sample showed a direct bandgap of 1.4(1) eV, indicating the semiconducting nature. The thermal conductivity study showed that polycrystalline Ba3.2Sn0.6Bi2.4S8 has an extremely low thermal conductivity of ∼0.30 ​W/mK at 773 ​K. The first-principles theoretical studies of electronic structure and nature of chemical bonding in Ba3Sn0.62Bi2.38S8 are performed within the framework of DFT. © 2022 Elsevier Inc.