Two new organic nonlinear optical (NLO) materials of hydroxyethylammnonium-L-tartrate monohydrate (HOH2CH2CNH3+ center dot HOOCHC (OH)HC(OH)COO-center dot H2O, HALT) and hydroxyethylammonium-D-tartrate monohydrate (HOH2CH2CNH3+center dot HOOCHC(OH)HC (OH)COO-center dot H2O, HADT)have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction, and further identified by element analyses, FT-IR spectra and TG/DTA measurements. Solubility curves of HALT and HADT have been determined in water. The bulk crystals of HALT and HADT were obtained using slow-cooling method. Morphological analyses, the ultraviolet-Vis-NIR transmission spectra, and the nonlinear optical properties of the two crystals were studied. (c) 2006 Elsevier B.V. All rights reserved.