The double T-junction microchannel is a classical microstructured chemical device used to generate gas/liquid/liquid three-phase microflows. An experimental study that focused on the three-phase flow phenomena and bubble/droplet generation rules in a double T-junction microchannel was introduced. Based on the published knowledge of gas/liquid and liquid/liquid two-phase microflows, new flow patterns were carefully defined: bubble cutting flow, spontaneous break-up and bubble cutting coupling flow, and bubble/droplet alternate break-up flow. According to the classical correlations of bubble and droplet volumes and their generation frequency ratio, the operating criteria for creating different three-phase flow patterns were established and a model for the dimensionless average bubble and droplet volumes in the three-phase microflows was developed. These various three-phase microflows have great application potential in material science and flow chemistry synthesis. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 1722-1734, 2015