New experimental data on the thermal conductivity of trans-1-chloro-3,3,3-trifluoropropene (R1233zd(E)) are reported that allow the development of wide-range correlations. These new experimental data, covering a temperature range of 204 to 453 K at pressures from 0.1 to 67 MPa, are used to develop a correlation for the thermal conductivity. The experimental data reported here have an uncertainty of 1% for liquid and supercritical (density > 700 kg.m(-3)), 1.5% for vapor and supercritical (pressure > 1 MPa and density < 200 kg.m(-3)), 3% for supercritical (200 kg.m(-3) < density < 700 kg.m(-3)), and 3% vapor and supercritical (pressure <1 MPa). On the basis of the uncertainty of and comparisons with the present data, the thermal-conductivity correlation for R1233zd(E) is estimated to have a relative expanded uncertainty ranging at a 95% confidence level from 1% to 4% depending on the temperature and pressure with larger uncertainties in the critical region.