New experimental data on the thermal conductivity of pentafluoroethane (R125) are reported that allow the development of an improved wide-range correlation. These new experimental data, covering a temperature range of 190 K to 390 K and a pressure range of 0.1 to 70 MPa, are used together with available data from the literature to develop a correlation for the thermal conductivity of R125 that covers the temperature range from 190 K to 512 K. The experimental data reported here have an uncertainty of less than 1% for measurements removed from the critical point and for gas at pressures above 1 MPa, which increases to 3 % in the critical region and for gas at low pressures (< 1 MPa). The quality of the primary data sets is such that the thermal conductivity correlation for R125 is estimated to have an uncertainty of about 3 % at a 95 % confidence level, with the exception of state points near the critical point and the dilute gas, where the uncertainty of the correlation increases to 5 %.