Semi-organic single crystals of guanidinium tris cadmium sulphate octahydrate (GuCdS) with nonlinear optical properties were successfully grown by slow solvent evaporation technique. The grown crystals were characterised by powder X -ray diffraction analysis to determine the unit cell parameters. The structure of the compound belongs to triclinic crystal system and space group is found to be P1. The grown crystals were subjected to FTIR spectroscopic analysis to confirm the presence of functional groups present in the compound. UV-vis-NIR spectral study suggested that the grown crystal is transparent in the entire visible region, the lower cut off wavelength is 200 nm and the band gap value is estimated to be 6.14 eV. Nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) were calculated using Z-scan technique. The thermal stability of grown crystal was investigated by thermogravimetric and differential thermogravimetric analyses. The dielectric behaviour of the grown crystal was analyzed as a function of frequency of the applied field. The mechanical properties of grown crystal were examined by Vickers′s micro hardness test. The laser damage threshold of the grown crystal was calculated to be 1.796 GW/cm2.