Densities of 1,1,1-trifluoroethane (R-143a) have been measured using a vibrating-tube densitometer over a density range from 41 kg . m-(3) to 1113 kg . m(-3) along 15 isotherms between 263 K and 403 K and at pressures between 1.5 MPa and 15 MPa. The experimental uncertainties of the measurements are estimated to be +/-5 kPa in pressure, +/-11 mK in temperature, and +/-0.3% to +/-2% in density.