 This research examined the effect of micro-channel diameter on electro-osmotic flow hysteresis. The results showed that smaller channels exhibited greater hysteresis than larger ones, due to the coupling effect of the wider slash tighter interfacial width and the minority pH governed ion-driven hysteresis. This knowledge could be used to optimize chemical and biological microfluidic systems with adjustable throughput. This article was authored by Anning Lim and Cherine Goh.