The new ternary selenostannates Sr4Sn2Se9 and Sr4Sn2Se10 have been synthesized by heating the elements at 1023 K in an argon atmosphere. Their structures were determined by single-crystal X-ray methods. Sr4Sn2Se9 crystallizes in a new structure type (Pbam, a = 12.042(2) Angstrom, b = 16.252(3) Angstrom, c = 8.686(2) Angstrom, Z = 4) with Sn2Se64-, SnSe44-, and Se-2(2-) subunits. Sr4Sn2Se10 (P2(1)2(1)2, a = 12.028(2) Angstrom, b = 16.541(3) Angstrom, c = 8.611(2) Angstrom, Z = 4) has a similar structure with Se-3(2-) triangles instead of Se-2(2-) dumbbells. Strontium is 8-fold-coordinated by selenium in both cases. The opening angles between tin and the terminal selenium atoms in the Sn2Se6 subunits are close to 1600, which. is nearer a typical Sn2+ coordination geometry than classical SnSe4 tetrahedra. This result suggests the tin oxidation state in the Sn2Se6 Units to be lower than the expected Sn4+. This question is examined by self-consistent LMTO and LAPW band structure calculations expanded by the Bader analysis of the charge density to assign reliable atomic charges.