An impressive, nonlinear optically active single crystal, acid potassium hydrogen fumarate (2KC4H3O4.C4H4O4)(APHF)was grown by slow evaporation technique. Single crystal X-ray diffraction analysis confirms packing array and attribute of molecular geometry. FTIR and FT Raman studies aid to identify basic functional groups present in the crystal. UV–Vis spectral analysis predicts cut off wavelength as 295 nm. The Photo luminescence spectra shows an emission around 453 nm and its lifetime was also detected. Low dielectric constant of APHF can be utilized for microelectronics device fabrications. Vicker's microhardness test reveals the greater mechanical strength of APHF. TG and DSC studies shows thermal stability up to 253 °C.The total charge spread is described by Molecular electrostatic potential. Low HOMO-LUMO energy gap affirms the chemical softness of the material. The negative third order nonlinear parameters like refractive index (n2), absorption coefficient (β) and susceptibility (χ3) were estimated by Z-scan studies. © 2020 Elsevier B.V.