Single crystals of zinc guanidinium sulfate have been grown from solution by the slow evaporation technique. As-grown crystals were characterized by the X-ray diffraction analysis and the vibrational frequencies of various functional groups in the crystals have been derived from the Fourier transform infrared (FTIR) spectrum. Transmission range of the crystal was determined by UV-vis-NIR spectra. The nonlinear optical (NLO) property of the grown crystal was confirmed by the Kurtz-powder SHG test. Thermal analysis was performed to study the thermal stability of the grown crystals. The hardness of the grown crystal was studied using Vickers microhardness tester. (C) 2009 Elsevier B.V. All rights reserved.