Single crystals of nonlinear optical material bis (guanidinium) hydrogen phosphate monohydrate (G2HP) belonging to non centrosymmetric space group P 21c were successfully grown by the slow evaporation method. Optical transmittance and second harmonic generation of the grown crystals have been studied by UV-vis-NIR spectrum and Kurtz powder technique respectively. The transmittance of G2HP crystal has been used to calculate the refractive index (n), the extinction coefficient (k), reflectance (R) and both the real (εr) and imaginary (εi) components of the dielectric constant as a function of wavelength. The anisotropic mechanical behavior and dielectric response of G2HP has been analyzed.