The first X-ray diffraction and vibrational spectroscopic analysis of a novel complex between L-lysine and L-tartaric acid is reported. The structure was solved in two temperatures (320 and 260 K) showing incommensurate phase between them. Room-temperature powder infrared and Raman measurements for the L-lysine-L-tartaric acid molecular complex (1: 1) were carried out. DSC measurements on powder samples indicate two phase transitions points at about 295, 300 and 293, 300K, for heating and cooling, respectively, with noticeable temperature interval between them. Second harmonic generation efficiency d(eff) = 0.35 d(eff) (KDP). (c) 2005 Elsevier Inc. All rights reserved.