Prismatic single crystals of novel compounds BaLaSi2 and Ba5LaSi6 were synthesized from the elements with or without a Na flux. The crystal structures of the compounds were analyzed by X-ray diffraction. BaLaSi2, containing cis-trans (1)(infinity)[Si] chains, crystallizes in an orthorhombic cell (a = 4.6414(2) angstrom, b = 14.8851(7) angstrom, c = 6.7519(5) angstrom; space group, Cmcm (No. 63), Z = 4) and is isotypic with the low-temperature phase of LaSi. The crystal structure of Ba5LaSi6 (a = 17.1447(5) angstrom, b = 4.8767(1) angstrom, and c = 17.9102(4) angstrom; space group Pnma (No. 62), Z 4) is a new type containing isolated anionic groups ((0)[Si-5-Si]) of a pentagonal Si ring with a Si-Si stem. The electrical resistivities measured for the polycrystalline BaLaSi2 and Ba5LaSi6 sintered samples were 0.31 and 0.48 m Omega.cm, respectively, at 300 K and increased with temperature. The Seebeck coefficients of BaLaSi2 and Ba5LaSi6 were -7.6 and -11 mu V.K-1, respectively, at 296 K.