Single crystals of potassium p-nitrophenolate dihydrate (NPK (.) 2H(2)O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d(eff) of about 1.5 times that of lithium niobate and in which the K+ ions are bonded to the nitro group instead of bonding with the phenolic O-. Large single crystals of dimension upto 20 x 6 x 4 mm(3) are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 degrees C. Microhardness measurements on the cleaved plane (110) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser. (c) 2005 Elsevier B.V. All rights reserved.