A remarkably good second and third-order nonlinear optical (TONLO) single crystal potassium hydrogen phthalate magnesium sulfate (KHPMS) has been grown effectively using aqueous solution by conventional solution growth method. Single crystal XRD studies exhibits the crystal structure as triclinic with space group P1 for the grown KHPMS crystal. Crystalline nature of the title compound has been confirmed by powder XRD studies and by using Scherer formula particle size has been evaluated. Elemental analysis with CHNS mode authenticates the occurrence of carbon, hydrogen and sulphur in the grown crystal. The optical transmission study proves the transparency of the sample in the entire visible region and band gap has been determined using Tauc’s plot. The output intensity of SHG was verified by Kurtz and Perry powder technique and it was found to be 0.409 times as that of KDP. TONLO properties such as nonlinear refraction (NLR), nonlinear absorption (NLA), third-order susceptibility (χ3) and hyperpolarizability (γ) were calculated with high accuracy using Z-scan technique. THG effectively attributes to self-defocusing effect with high third-order susceptibility compared with other NLO crystals
