This paper presents criteria for the design of a flow distributor for even distribution of gas and liquid flows over parallel microchannels. The design criteria are illustrated for the case of a nitrogen-water Taylor flow (1 <ReGL <30 and 3 × 10-5 <CaGL <4 × 10-4) in four parallel microchannels of 0.9 mm inner diameter. The distributor consists of a gas manifold, a liquid manifold, four barrier channels for the gas and four for the liquid, and four T-mixers for mixing of the gas and liquid flows. The four barrier channels have equal inner diameters and length; four different diameters have been studied: 0.05, 0.1, 0.15 and 0.2 mm. Uniform distribution of the gas and liquid flows over the microchannels is achieved when the pressure drop over the barrier channels is in the range of around 4 to 25 times the pressure drop over the corresponding T-mixers and microchannels. Gas-liquid channeling is prevented at equal pressures in the gas and liquid manifolds. An optimal operational window is realized when the gas to liquid flow ratio kept constant and the ratio of the maximum over the minimum flow rates remain less than 20. The effect of variations in the inner diameters (result of the fabrication process) of the barrier channels and the microchannels on the flow distribution is demonstrated. It is suggested that these design criteria can also be applied at larger numbers of parallel microchannels.