The growth of optical quality single crystals of L-arginine perchlorate C6H14N4O2. HClO4 (abbreviated as LAPCI), 3 having dimensions 20 x 8 x 2 min, is reported. Crystals were grown from its aqueous solution of pH 8 at constant temperature by solvent evaporation technique. The grown crystals were charactefized by single crystal X-ray diffraction analysis, Fourier transform infrared and UV-VIS-NIR spectral studies. Thermal stability of the crystal is investigated using thermo-gravimetric analysis. SHG efficiency of LAPCI is found to be 3.12 times that of quartz. (C) 2004 Elsevier B.V. All rights reserved.