Four new rare earth gallosilicates, Rb2REGaSi4O12 (RE = Y, Eu, Gd, and Tb, denoted as REGS-1), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. They are the first examples of rare earth gallosilicates that contain individually occupied tetrahedral Ga3+ and Si4+ centers. The unique structure is formed of two 1 D and one 2D substructural units: unbranched achter single chains which are seldom observed in silicates, the PaCl5-type infinite chains formed of edge-sharing REO7 petagonal bipyramids and the unprecedented mixed-anion double layers with the composition [GaSi4O12]. The photoluminescence properties of EuGS-1 and TbGS-1 have been studied. The Y3+ ion in YGS-1 can be partially replaced by Eu3+ and Tb3+ to yield luminescent materials.