Characteristics of air-water two-phase flow in a mini-square-channel were investigated experimentally. One sidewall of the flow channel was made of permeable porous material (carbon paper). Air was fed into the channel from its inlet, while water was injected uniformly into the channel along the permeable wall. Based on the observed results, flow patterns of this special gas-liquid two-phase flow were classified, and different kinds of surface characteristics of the permeable wall were used, flow regime maps for specific flow parameters were drawn, and the influence of different combinations of gas flow rate and liquid infiltration amount on flow patterns were also analyzed. Meanwhile, the paper also provided a detailed analysis of the channel pressure drop characteristics in this kind of two-phase flow; with special focus on the influence of different kinds of permeable wall surface characteristics on pressure drop variation. (C) 2013 Published by Elsevier Ltd.