Tetra-n-butyl ammonium bromide (TBAB) is a tetra-alkylammonium salt, that forms two types of semiclathrate hydrate. At atmospheric pressure, the melting points are between room temperature and freezing point of water. There are some useful applications of the semiclathrate, for example using as a heat transport medium and gas separator, but there are little knowledge about TBAB hydrates characteristics. In this paper, some thermal properties of TBAB semiclathrate hydrate are reported. We determined the phase diagram of semiclathrate hydrate nucleation under the condition of atmospheric pressure, latent and specific heats capacity of TBAB semiclathrate hydrate. From the phase diagram, the congruent melting points of two TBAB hydrates were determined. Using above results, we obtained the hydration numbers of two type TBAB hydrates. (c) 2005 Elsevier B.V. All rights reserved.