A lithium gadolinium phosphate crystal, LiGd5P2O13, has been synthesized by a high temperature solution reaction and solved by single-crystal X-ray diffraction data. The structure is monoclinic, space group C2/m, with unit cell parameters a = 18.645(3), b = 5.6257(5), c = 12.014(2) angstrom, beta = 117.55(6)degrees, V = 1117.3(3) angstrom(3), and Z = 4. LiGd5P2O13 presents a new structural type and is built up from [Gd5P2O13](-) layers and one-dimensional Li chains with an unusual Li-Li distance. The optical properties were investigated in terms of the absorption and emission spectra. Additionally, the calculations of band structure, density of states, dielectric constants, and refractive indexes were performed with the density functional threory method. The obtained results tend to support the experimental data.