Experiments on a steam-air mixture flowing in a vertical tube were carried out to understand a temperature distribution in the tube and to accumulate a database of condensation heat transfer of the steam-air mixture. The condensation tube used was 49.5 mm in diameter and 510 mm long. The ratio of inlet mass fluxes of air and steam was 3:2. They were mixed at a mixing section and flowed into the condensation tube at fully-developed conditions through a straight tube. The water flowing in the outside of the condensation tube cooled the steam-air mixture. The pressure was 0.125 MPa at the inlet of the tube. The experiments were carried out at two different inlet air temperatures and at three different Reynolds numbers. The temperature was measured at 11 points in the radial direction and 7 levels in the vertical direction in the condensation tube. The local heat fluxes were evaluated from temperature distributions measured in the tube wall. Experimental data showed that the heat transfer coefficient h decreased in the flow direction except when flow at the inlet was in the saturated condition. Vierow & Schrock's correlation well evaluated the decrease trend of hc in the flow direction, however, it failed in evaluating dependence of h on the Reynolds number Rem. Siddique's correlation takes the radial distribution of mass fraction of non-condensable gas into account, which well evaluated the dependence of h on Re . This result implies that the hc correlations should take into account axial and radial distributions of the mass fraction of non-condensable gas as well as liquid film thickness. c c c m