A colourless single crystal of Li3Cs2B5O10 with dimensions of 20 x 15 x 4 mm(3) has been grown. It was obtained from the stoichiometric melt using the top-seeded solution growth method in air. The infrared spectroscopy data, density and hardness of the Li3Cs2B5O10 crystal were measured. The measured density is in agreement with the calculated one and the hardness is about 4 Mohs. The GII value is larger than the BSI value, indicating that the lattice-induced strain is stronger than the electronic strain. Using the structural parameters of the single crystal Li3Cs2B5O10, we present a first-principles study of its electronic structure. The calculated band structures and the density of states of Li3Cs2B5O10 suggest that its indirect energy gap is 5.16 eV. The linear optical properties are examined based on the dielectric function. Our calculated bond lengths show a reasonable agreement with the experimental data.