Potassium hydrogen malate monohydrate (PHMM), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from aqueous solution. Single crystals of PHMM have been grown by slow evaporation of solvent at room temperature up to dimensions of 22 mm x 16 mm x 14 mm. Single-crystal X-ray diffraction study on grown crystals shows that they belong to monoclinic system and non-centrosymmetry spacegroup Cc. The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectroscopic study was performed for the identification of different modes of functional groups present in the compound. The UV-Vis transmission spectrum has been recorded in the range 200-1100 nm. The thermal stability of the compound has been determined by TG-DTA curves. The dielectric studies were performed. From the microhardness measurements, Vicker's hardness number (H-v), Stiffness constant (C-11), fracture toughness (k(c)), Brittle index (B-i) and yield strength (sigma(y)) have been calculated. The Young's modulus was calculated using the Knoop hardness measurement. The SHG relative efficiency of PHMM crystal was found to be 1.2 times higher than that of KDP. (C) 2008 Elsevier B.V. All rights reserved.