Single crystals of sodium-substituted lithium paranitrophenolate trihydrate (Na-NPLi center dot 3H(2)O) having dimensions upto 16 x 8 x 4 mm 3 have been successfully grown by slow evaporation technique. The grown crystals are confirmed by XRD and FTIR analyses. Optical absorption and NLO studies reveal the increase in NLO activity of this crystal in the presence of sodium. Thermal studies brings forth that the crystals are stable upto 180 degrees C. Microhardness measurements on the cleaved planes (1 1 0) and (1 0 1) verifies the anisotropic behaviour of the crystal. (c) 2005 Elsevier B.V. All rights reserved.