Single crystals of L-lysine hydrochloride dihydrate (LLHCD), a nonlinear optical material, have been grown by slow cooling technique from its aqueous solution. LLHCD was found to be highly soluble in water. The grown crystals have been subjected to single crystal X-ray diffraction to confirm the structure and to estimate the lattice parameters. The vibrational structure of the molecule is elucidated from FTIR spectra. Thermal analysis revealed the thermal stability of the grown crystals. The optical transmittance spectrum shows that the material possesses good optical transparency in the entire visible region with a UV cut-off wavelength at 228 nm. The mechanical properties of the grown crystal have been studied using Vicker's microhardness test. The laser damage threshold of 52.25 MW/cm(2) has been measured by irradiating Q-switched Nd:YAG laser (1064 nm). (c) 2007 Elsevier Ltd. All rights reserved.