Semi-organic nonlinear optical single crystals of pure, Ni(2+) and Cd(2+) doped L-Lysine monohydrochloride dihydrate (L-LMHCl) were grown from aqueous solution by slow evaporation technique. Single crystal Xray diffraction analysis reveal that the pure and doped L-LMHCl crystals belong to monoclinic system with the space group P2(1). The presence of functional groups present in the pure and doped crystals was determined qualitatively by using Fourier Transform Infrared (FTIR) spectroscopy. Optical absorption studies reveal very low absorption for the doped crystal than that of the pure crystal. Dielectric studies have been carried out for the grown crystals and the results were discussed in detail. (C) 2009 Elsevier B.V. All rights reserved.