An organic nonlinear optical single crystal of L-histidinium glutarate monohydrate (LHG), has been synthesized by slow solvent evaporation method at an ambient temperature. Single crystal X-ray diffraction technique was employed to find the structure of the grown compound. The elemental composition of the compound was confirmed by Energy dispersive X-ray analysis. Molecular structure of LHG was established by proton NMR and carbon NMR spectral studies. The optical absorption coefficient α was analyzed from the UV spectral analysis and the optical band gap of the compound was estimated. The nonlinear optical property was confirmed by the powder technique of Kurtz and Perry.