Data from the Mariner 1969 radio occultation measurements are utilized to derive altitude profiles for the refractivity, the free electron number density, and the plasma temperature above the occultation points. Initial results indicate that the ionosphere was denser and warmer in 1969 than during the quiet solar conditions prevailing at the time of the Mariner 4 encounter with Mars in 1965. The dayside ionosphere consists of two layers with peak densities of the order of 7×104 and 1.7×105 electrons/cm3 at 110- and 135-km altitude, respectively. Assuming that CO2+ is the principal ion in the main layer yields a topside plasma temperature of 400°—500°K. A marked change in the scale height near 250 km may reflect the transition to a lighter ion such as CO+ No clear signature of nighttime ionosphere was observed.