Comprehensive and accurate measurements of the saturated-liquid and saturated-vapour densities together with the vapour pressure of pure ethylene were carried out from T = 104 K (triple-point temperature T-t = 103.989 K) to 0.025 K below the critical temperature. The critical constants (T-c = 282.350 K, rho(c) = 214.24 kg . m(-3), p(c) = 5.0418 MPa) and the isothermal compressibilities in the critical region close to the phase boundary have also been determined from these measurements. Comparisons with experimental results of previous workers are presented. Based on the new values from this work, new correlation equations for the vapour pressure, the saturated-liquid density, and the saturated-vapour density have been established.