This paper presents an experimental investigation on the flow patterns of Newtonian/non-Newtonian fluids two-phase flow in T-shaped rectangular microchannels by using a high-speed camera. Three different dimensions of microchannels are employed with 400 mu m x 400 mu m, 400 mu m x 600 mu m, 400 mu m x 800 mu m in depth and width, respectively. The cyclohexane is used as the dispersed phase, and various concentrations of carboxyl methyl cellulose (CMC) aqueous solutions as the continuous phase. Results show that slug flow, droplet flow, parallel flow and jet flow are the main flow patterns for cyclohexane-CMC two-phase flow in rectangular microchannels. The larger the concentration of CMC solutions and the smaller the size of the microchannels are, the wider of the regimes are for the droplet flow and parallel flow. A model is proposed to predict the transitions between adjacent flow regimes for liquid-liquid two-phase flow in non-Newtonian fluids in rectangular microchannels. (c) B.V 2015 Elsevier B.V. All rights reserved.