The behavior of air-water two-phase flow at a horizontal micro-T-junction with main and side branch of 500 pm diameter was studied in this work. When the inlet flow pattern was a slug-annular flow, the impact of varying of upstream gas and liquid superficial velocity on phase distribution of two-phase flow in the T-junction was investigated in detail. It is found that the liquid taken off decreases as an increase in liquid superficial velocity, while it increases as an increase in gas superficial velocity. Liquid and gas superficial velocity have stronger impact on phase distribution when the inlet gas velocity is high. When the present data are compared to those from larger diameter T-junctions at similar inlet superficial velocities, it is found that decreasing the diameter of T-junctions increases the fraction of liquid taken off. (C) 2010 Elsevier Ltd. All rights reserved.