The far-infrared THz spectra of naphthalene, alpha-naphthol, beta-naphthol, biphenyl and anthracene have been measured using THz time-domain spectroscopy. The low-energy vibrational modes of measured molecules are discussed based on their characteristic and common features. The complex dielectric functions are obtained. Meanwhile, it is shown that the experimental results can be well fitted by a standard Lorentz model. (C) 2004 Elsevier B.V. All rights reserved.