Three new rare-earth (RE) niobium stannides, namely, Sc2Nb4-xSn5 (x = 0.37, 0.52), YNb6Sn6, and ErNb6Sn5, have been obtained by reacting the mixture of corresponding pure elements at high temperature and structurally characterized by single-crystal X-ray diffraction studies. Sc2Nb4-xSn5 crystallizes in the orthorhombic space group Ibam (No. 72) and belongs to the V6Si5 type. Its structure features a three-dimensional (3D) network composed of two-dimensionally (2D) corrugated [Nb2Sn2] and [Nb2Sn3] layers interconnected via Nb-Sn bonds, forming one type of one-dimensional (1D) narrow tunnels along the c axis occupied by Sc atoms. YNb6Sn6 crystallizes in the hexagonal space group P6/mmm (No. 191) and adopts the HfFe6Ge6 type, and ErNb6Sn5 crystallizes in the trigonal space group R $(3) over bar $m (No. 166) and belongs to the LiFe6Ge5 type. Their structures both feature 3D networks based on 2D [Nb3Sn], [Sn-2], and [RESn2] layers (RE = Y, Er). In YNb6Sn6, one type of [Nb3Sn] layer is interconnected by [Sn-2] and [YSn2] layers via Nb-Sn bonds to form a 3D network. However, in ErNb6Sn5, two types of [Nb3Sn] layers are interlinked by [Sn-2] and [ErSn2] layers via Nb-Sn bonds into a 3D framework. Electronic structure calculations and magnetic property measurements for "Sc2Nb4Sn5" and YNb6Sn6 indicate that both compounds show semimetallic and temperature-independent diamagnetic behavior.