This paper presents measurements of vapor pressure from 220 K to 338 K, liquid density from 180 K to 350 K and up to 70 MPa and vapor density from 310 K to 480 K and up to 12 MPa for pentafluoroethane (R-125). Extrapolating the observed vapor pressures to the measured critical temperature (339.41 +/- 0.01) K provides a critical pressure of (3.6391 +/- 0.002) MPa. Using these values with the law of rectilinear diameters indicates a critical density of (4768 +/- 7) mol.m(-3) Correlations provide values which agree with the measured values for the vapor densities within +/- 0.05%, the liquid densities within +/- 0.1%, and the vapor pressures within +/- 0.05%. The results are compared with values from the Literature.