The speed of sound of the gaseous trifluoroiodomethane (CF3I) was measured for temperatures from 273.15 to 333.15 K and pressures from 58 to 276 kPa with a cylindrical, variable-path acoustic interferometer operating at 156.252 kHz. The uncertainty of the speed of sound was less than +/-0.1%. The ideal-gas heat capacity at constant pressure and the second acoustic virial coefficients were determined over the temperature range from the speed of sound measurements. The ideal-gas heat capacity at constant pressure and second virial coefficients calculated from the present speed of sound measurements were compared with the available data. The uncertainty of the ideal-gas heat capacity at constant pressure was estimated to be less than +/- 1%.