Abstract The infrared, the Fourier transform infrared and Fourier transform Raman spectra of p-chlorobenzoic acid ( p-CBA) has been recorded in the region 4000–600 cm −1, 4000–400 cm −1 and 4000–100 cm −1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of p-CBA were obtained by the ab initio HF and DFT (B3LYP) methods with complete relaxation in the potential energy surface using 6-311+G(d,p) basis set. The harmonic-vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.