Two novel indium silicates, K5In3Si7O21 (1) and K4In2Si8O21 (2), have been synthesized by a flux-growth method and characterized by single-crystal X-ray diffraction. The structure of 1 consists of siebener single chains of corner-sharing SiO4 tetrahedra running along the b axis linked via corner-sharing by In2O9 face-sharing octahedral dimers and InO5 trigonal bipyramids to form a 3D framework. The structure of 2 consists of a 3D silicate framework containing 6- and 14-ring channels. InO5 square pyramids are located within the 14-ring channels sharing corners with the silicate framework. The solid-state Si-29 MAS NMR spectrum of compound 1 was recorded; it shows the influence of the indium atoms in the second coordination sphere of the silicon on the chemical shift. Crystal data: 1, orthorhombic, Pna2(1) (No. 33), a = 12.4914(3) angstrom, b = 16.8849(3) angstrom, c = 10.2275(2) angstrom, V = 2157.1(1) angstrom(3) and Z = 4; 2, monoclinic, P2(1)/n (No. 14), a = 8.4041(3) angstrom, b = 11.4919(4) angstrom, c = 10.4841(3) angstrom, beta = 90.478(2)degrees, V = 1012.5(1) angstrom(3) and Z = 2.