A new polymorph of SrS3 was obtained by a reaction of SrS and S with an atomic ratio of Sr:S = 1:5 under a pressure of 5 GPa at 1200 degreesC. It crystallized in a tetragonal unit cell with a = 6.708(1) Angstrom, c = 3.942(1) Angstrom, and V = 177.36(6) Angstrom(3). It was isotypic with BaS3, and contained S-3(2-) polysulfide ions. The product obtained from the high-pressure synthesis contained an amorphous component. It was highly deliquescent and formed a yellowish solution. A new layered polysulfide, Sr-2(OH)(2)S-4.10H(2)O, crystallized in the solution. The sulfide belonged to a triclinic space group of P (1) over bar (No. 2) with lattice constants of a = 5.9107(5) Angstrom, b = 7.8682(6) Angstrom, c = 9.4134(6) Angstrom, alpha = 75.639(6)degrees, beta = 73.824(3)degrees, gamma = 71.639(3)degrees, V = 392.83(5) Angstrom(3), and Z = 1. Each Sr ion was coordinated with one OH ligand and eight H2O ligands. Six H2O ligands out of the eight were bridging ligands to form two-dimensional [Sr-2(OH)(2)(H2O)(10)(2+)](infinity) cationic layers, between which S-4(2-) tetrapolysulfide ions were situated. The S-4(2-) anion had a coplanar configuration with a dihedral angle of 180.0degrees, The stability of S-4(2-) anions having different conformations was discussed from a viewpoint of ab initio MO calculations on changing the dihedral angles of S-4(2-).