Abstract Time domain terahertz (0.2–2 THz) and FTIR (400–4000 cm−1) spectra of ‘Bisphenol A’ are presented. An average refractive index of 1.34 from 0.2 to 2 THz and an absorption peak at 1.69 THz that is considered as the twisting of aromatic rings with hydroxyl groups along the shared carbon atom are found. The simulated results by using density functional theory (DFT) with B3LYP 6-311++G (3df, 3pd), B3LYP 6-31G (3df 3pd) and B3LYP 3-21G after anharmonic corrections are well agreed with the experimental results. Furthermore, Pulay’s Method is adopted to overcome the incapability of DFT in describing C–H and O–H stretching interactions to match with experimental values.