A UV transmittable NLO crystal Hydrofluoric acid mixed Sulphamic acid (FASA) was synthesized and explored in aqueous solution by slow solvent evaporation technique at ambient temperature. Centimeter sized 3 × 2.8 × 1 cm3 crystal was harvested in a period of 25-30 days. Single crystal X-ray diffraction data manifest FASA crystallizes in Tetragonal P crystal system with lattice parameters of a = 8.12 Å, b = 8.12 Å, c = 9.29 Å and α=β=γ =90̊. The peaks in powder X-ray diffractogram were indexed corresponding to the (hkl) plane orientations showing the crystalline purity and perfection. FTIR spectrum authenticate the functional groups exist in FASA crystal system. UV-vis-NIR spectrum validated a wide transparency range with short UV cut-off edge closer to 200 nm. FASA endowed with larger dielectric polarizability. Kurtz-Perry powder test flashed the Phase matchable SHG efficiency 0.43 times KDP. Soft nature of FASA suits itself for crystal feasibility. The presence of HF with sulphamic acid delivered a mixed crystal system FASA suitable for UV nonlinear optical applications.