This study examines the venting gas characteristics in a microchannel through a hydrophobic nanoporous membrane with a pore size of 0.22 μm and a porosity of 70%. A total of three microchannels were made and tested, including a serpentine, a parallel and a contraction-expansion configuration. The mass flux (G) is 5, 7.5 and 10 kg/m
s with the quality (x) ranging from 0 to 0.1. Flow visualization is also performed to observe the bubbles movement under different experimental conditions. The tested results show that the amount of venting gas is strongly related to the contact time and configuration of gas slug and the development of flow pattern in the channel.