Five　new　semiconductors　Pb5Sb12+xBi6-xSe32　(x　=　0,　1,　2,　3,　and　4)　have　been　synthesized　for　the　first　time,　which　adopt　pavonite-type　structure　and　crystallize　in　monoclinic　C2/m　space　group.　The　crystal　structure　is　composed　of　two　different　types　of　polyhedral　slabs.　Slab-I　is　a　galena-like　structure　motif　that　forms　with　[MSe6]　(M　=　Pb,　Sb,　and　Bi)　octahedra　and　slab-II　contains　one　octahedral　[MSe6]　block　and　paired　squared　pyramids　[MSe5].　Pb5Sb12+xBi6-xSe32　exhibits　n-type　semiconductor　behaviors　and　the　remarkable　Seebeck　coefficient　from　-64.1　mu　V　K-1　for　x　=　0　sample　to　-242　mu　V　K-1　for　x　=　4　sample　at　300　K.　Moreover,　the　Pb5Sb12Bi6Se32　has　the　highest　carrier　concentration　of　1.35　x　10(20)　cm(-3)　in　pavonite-type　materials.　The　complex　compositions,　mixed　occupancies　of　the　cations,　and　quasi-two-dimensional　structure　lead　to　the　low　lattice　thermal　conductivity　(kappa(lat))　less　than　0.48　W　m(-1)　K-1　from　300　to　723　K,　at　which　Pb5Sb16Bi2Se32　especially　shows　the　ultralow　value　of　0.25　W　m(-1)　K-1.　As　a　result,　the　thermoelectric　figure　of　merit,　ZT　similar　to　0.34　at　723　K,　is　obtained　for　the　intrinsic　Pb5Sb12Bi6Se32.