A non-centro symmetric single crystal of Urea Oxalic acid (UOA) has been grown from aqueous solution by the process called slow evaporation technique. Single crystal X-ray diffraction (SXRD) evinces UOA corresponding to the triclinic crystal system with the space group P. The diverse functional groups existing in UOA are vividly discovered with Fourier transform infrared (FTIR) and FT-Raman spectrum analysis. Ultraviolet (Uv)-visible spectral analysis reveals that the crystal has the cut-off wavelength of 263 nm. The thermal stability of the grown crystal has been studied by thermo gravimetric analysis and differential scanning calorimetric technique. The Vicker's micro hardness test was also carried out employing one of the as-grown crystals are assessed. The dielectric behavior of the grown crystal was thoroughly analyzed for different temperatures. Fluorescence emission spectrum (PL) has been recorded and lifetime was also studied. The scanning electron microscope (SEM) technique was also carried out and determined the surface morphology topography of the UOA crystal. The theoretical study has been done by quantum mechanical calculations of DFT using Gaussian software package. The structural, vibrational and electronic properties of the title compound had been presented using the B3LYP method with 6-311++G (d, p) basis set. The linear polarizabilities (α) and the first order hyperpolarizability (β) values of the investigated molecule have been calculated. The HOMO-LUMO energies show that the chemical activity of the molecule and molecular electrostatic potential maps (MEPs) and NLO activity confirm to the superiority of the material. The third order nonlinear optical characteristics of UOA have been investigated using z-scan technique. © 2018 The Physical Society of the Republic of China (Taiwan)