The compound Ba3ThSe3(Se2)2 has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of 18[Th(Se)3(Se2)26-] separated by Ba2+ cations. Each Th atom in these chains is coordinated to two Se-Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th-Se distances are consistent with Th4+ and hence charge balance of Ba3ThSe3(Se2)2 is achieved as 3×Ba2+, 1×Th4+, 3×Se2-, and 2×Se22-. From optical measurements the band gap of Ba3ThSe3(Se2)2 is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor. © 2015 Elsevier Inc.