Single crystals of non-linear optical L-threonine amino acid have been grown by slow evaporation and temperature-lowering methods from aqueous solution. As-grown crystals were characterized by powder X-ray diffraction analysis and the vibrational frequencies of various functional groups in the crystals have been derived from FTIR spectrum. The range and percentage of optical transmission is assertained by recording UV-VIS-NIR spectrum. Thermal behaviour of the crystals has been investigated by DSC and TGA analyses. The NLO property of the grown crystal has been confirmed by Kurtz-powder SHG test. (C) 2004 Elsevier B.V. All rights reserved.