The guanidinium perchlorate crystals were grown from aqueous solution by low temperature solution growth technique. The cell parameter values were found out using X-ray diffraction analysis. The presence of chlorine in guanidine perchlorate was estimated qualitatively by FTIR analysis. The optical transmittance window and the lower cutoff wavelength have been identified by UV-vis-NIR spectral analysis. Second harmonic generation efficiency is found to be 1.5 times that of KDP. Thermal stability of the crystal was investigated using thermo-gravimetric analysis. Microhardness studies were carried out using Leitz-Wetzler hardness tester at room temperature. (C) 2011 Elsevier B.V. All rights reserved.