It is often assumed that the characteristics of airtightness of high-rise residential buildings are similar to those of typical detached houses. In high-rise residential buildings, however, air leakage happens not only by the exterior windows but also by the interior walls between dwellings. Moreover, there is many factors that have influences upon the air leakage in high-rise building. Therefore, it is important to know the air leakage data or the criteria of leakage of residential units to estimate the energy loads. This paper presents the airtightness characteristics of dwelling units in two high-rise residential buildings and the limited conclusions that can be drawn from these data. Based on the measurement data, the main cause of the airtightness distinction between two residential buildings is due to the different envelope types.