In relation to the development of the interfacial area transport equation, axial developments of one-dimensional void fraction, bubble number density, interfacial area concentration, and Sauter mean diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured by using an image-processing method under microgravity environment. The flow measurements were performed at four axial locations (axial distance from the inlet normalized by the pipe diameter = 7, 30, 45 and 60) under various flow conditions of superficial gas velocity (0.0083-0.022 m/s) and superficial liquid velocity (0.073-0.22 m/s). The interfacial area transport mechanism under microgravity environment was discussed in detail based on the obtained data and the visual observation. These data can be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow under microgravity environment. (C) 2003 Elsevier Science Ltd. All rights reserved.