The relative permittivity (epsilon(r)) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the Er measurements is estimated to be better than 1.2 x 10(-2). A complete set of tables of experimental data as a function of temperature. pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of epsilon(r) on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (mu*). The apparent dipole moment obtained was mu(*) = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood-Frolich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent Calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the Values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements. (C) 2008 Elsevier B.V. All rights reserved.