The refractivity of carbon dioxide has been measured at 2.26 GHz under simulated Martian conditions and at standard temperature and pressure. In the temperature range of 150° to 190°K, at pressures from 2 to 25 millibars, the refractivity per molecule per cm2 is 1.78 × 10−17 ± 0.06 when scaled by the ideal gas law. The measurements include pressures and temperatures which are within 30°C of the sublimation curve. This result is slightly lower than the best measurements previously obtained near standard temperature and pressure at other frequencies (1.8345 × 10−17 ± 0.0003) and at 2.26 GHz under standard conditions by the authors (1.8413 × 10−17 ± 0.005). It is concluded that the scaled refractivity of CO2 in the range of temperatures and pressures stated above may be a few percent lower than under standard conditions. These results do not significantly alter the conclusions regarding the atmosphere of Mars as measured by the radio occultation method.