The new phases LiTiPO5 and LiTiAsO5 have been synthesized by solid state reaction. They are essentially isostructural with α-Fe2PO5, as confirmed by X-ray Rietveld refinement. The structures are built of chains of edge-sharing LiO6 octahedra cross-linked by chains of alternate corner-sharing PO4 tetrahedra and TiO6 octahedra (each of which shares common faces with two LiO6 octahedra). Unit cell dimensions: LiTiPO5, a = 7.4000(5) Å, b = 6.3752(3) Å, c = 7.2347(4) Å; LiTiAsO5, a = 7.5257(5) Å, b = 6.5786(4) Å, c = 7.4524(5) Å. Space group: Pnma. The phases melt incongruently at ∼1080°C and exhibit very low electrical conductivities, (5-10) × 10-6 S cm-1 at 400°C with activation energy ∼1 eV. Subsolidus phase diagrams for the systems Li2O-TiO2-P2O5/As2O5 are presented.