Stoichiometric oxidation of SmCl2 with sulfur in the presence of NaCl (evacuated silica vessel, 850 °C, 7 d) results in the formation of A—Sm2S3 (orthorhombic, Pnma (no. 62), a = 737.64(5), b = 397.44(3), c = 1536.26(9) pm, Z = 4, Rw = 0.017). In contrast, C—Sm2S3 (cubic, I43 d (no. 220), a = 844.71(3) pm, Z = 5.333, Rw = 0.017) is obtained upon reaction of the elements (Sm : S = 2 : 3) under otherwise analogous conditions. According to Sm2.67⬜0.33S4 it represents a defect-variant of mixed-valence Th3P4-type Sm3S4 (a = 852.39(3) pm, Z = 4, Rw = 0.013) which forms whenever reducing tantalum is used as container material instead of silica tubing. Ubiquitous oxidic impurities thereby also react to yield the oxygen-poor oxysulfides Sm10S14O (tetragonal, 141/acd (no. 142), a = 1485.96(4), c = 1974.04(8), Z = 8) and Sm2OS2 (monoclinic, P21/c (no. 14), a = 840.54(6), b = 706.20(5), c = 697.72(5) pm, β = 99.294(6)°, Ζ = 4, Rw = 0.024) as by-products. Regardless of the container material, NaCltype SmS (cubic, Fm 3 m (no. 225), a = 596.04(3) pm, Z = 4) emerges as product from equimolar oxidation of samarium with sulfur. Reactions of Sm2S3 with Sm2O3 in 1: 2 molar ratios are suitable to produce Ce2O2S-type Sm2O2S (trigonal, P 3 ml (no. 164), a = 389.25(3), c = 671.18(7) pm, Z = 1) even in tantalum capsules at 850 °C when some NaCl is added as a flux.