The crystallographic parameters, morphology, microhardness anisotropy and thermal properties including differential thermal analysis (DTA), thermo gravimetric analysis (TGA) of a new nonlinear optical material lithium paranitrophenolate trihydrate (NPLi(.)3H(2)O) are reported. The single crystals of NPLi(.)3H(2)O show effective phase matchable second harmonic generation properties for frequency conversion. Optically clear single crystals having dimensions up to 12 mm x 8 mm x 4 mm, have been grown successfully within a period of 60 days by isothermal solvent evaporation technique. The title compound crystallizes in monoclinic system with space group Pa. Microhardness measurement on different planes verifies the hardness anisotropy and thermal studies reveal good thermal stability of the material. The NLO property of the crystal is verified by employing Kurtz powder test. The crystal has a wide range of optical transparency from 400 nm to 1500 nm. (c) 2005 Elsevier B.V. All rights reserved.