Vibrational modes of a tetrahydrofuran (THF) in a clathrate hydrate (CH) are studied by Raman spectroscopy. Especially, we focused on around 900 cm(-1), where a CCCC stretching mode of THF is mainly observed. An asymmetric peak around 900 cm(-1), which shows a major CCCC stretching mode of THF with a minor tailing above 150K, is observed as clear four modes below 40K. We concluded that the peak-splitting is attributed to a restriction of vibrational motions of the guest molecule by the CH-cage wall at low temperature due to a deformation of a force field of the CH-cage for the guest molecule. (C) 2015 Elsevier B.V. All rights reserved.