Hydrothermal method successfully produced a new cesium-metal borate (CsKB4O5(OH)4·2H2O). The crystals are grown in the P21/c space group with a monoclinic lattice, a = 10.7298 (13) Å, b = 8.1521 (11) Å, c = 13.2690 (15) Å, _ = 108.325 (9)°, and Z = 4. The structure is composed of [B4O5(OH)4]2− groups connected to 8-coordinated potassium, 12- oordinated cesium ions, and water molecules forming the final 3D framework. FTIR and Raman spectra identified the type and nature of the borate groups within the structure. UV-Vis- NIR diffuse reflection spectra have studied the transmission property, whereas TG-DSC analyses revealed the thermal stability of the crystals. In addition, theoretical calculations have been executed to understand the density of states and band structure.