Colourless crystals of Li₂Ta₂O₃F₆ are obtained by heating a mixture of LiTaF₆ and LiTaO₃ in a sealed nickel tube to 700°C for 5 days, followed by slow cooling to room temperature. Li₂Ta₂O₃F₆ is also a product of controlled hydrolysis of LiTaF₆. It crystallizes in the trigonal space group P3₁21 with a = 558.11(3), c = 2096.10(4) pm, and Z = 3. The structure is built up by corner-sharing TaO₃F₃-octahedra forming anionic double layers parallel (001). The lithium cations are intercalated between these double layers having a square-pyramidal coordination by fluorine atoms. For the educt LiTaF₆ a new high-temperature modification was found, which is reversibly formed at 150°C. It crystallizes with a = 783.5 pm in the cubic NaSbF₆ type.