The breakup phenomena of large oil-in-water (O/W) emulsion droplets in silicon microchannel (MC) array devices at low applied pressures were investigated by microscopic and high-speed observations. This study used two sizes of MC arrays, each of which consisted of uniformity sized MCs, slit-like terraces, and deeply etched wells. Monodisperse feed O/W emulsion droplets that had entered the MC arrays were broken up into fine droplets primarily by snap-off that occurs due to localized shear inside the MCs and by pinch-off due to interracial tension effects inside the MCs or (in the inlet side or a terrace. The average droplet size or the permeate O/W emulsions depended significantly oil the MC size and exceeded the MC size by 1.2 to 1.4 times. Their coefficients of variation were 18% to 21%. The results obtained From preceding work were compared with the results for direct generation of O/W emulsion droplets using the same MC array device.