Microfluidic devices with microsieve array as the dispersion medium have been well recognized. However, few studies have been made on gas-liquid two-phase flow in microsieve dispersion devices. The bubble generation rules with single-pore, radial-array pores, axial-array pores, and square-array pores were systematically investigated. The rules of pore activation have been suggested by considering the capillary force, flow resistances of both dispersed phase and continuous phase. An empirical equation and a theoretical equation to predict the activation of pores in microfluidic devices were developed. An equation to correlate the average bubble diameter with parameter of channel structure, phase ratio, and Ca number of continuous phase was also developed. The strategy of design and scaling up for microsieve devices is proposed. Meanwhile, a device with dual-size pores according to the rules derived is designed. This device achieved much better dispersion performance. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 1663-1676, 2015