A complete vibrational spectrum analysis of p-chlorobenzenesulfonic acid has been performed. The wavenumbers are calculated on the basis of ab initio theory using Hartree-Fock/6-31G* basis set. The predicted infrared intensities, Raman activities and force constnats are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non linear optics. The calculated geometrical parameters are also in agreement with reported values.