This paper investigates the interfacial electrokinetic effects on characteristics of liquid flow through a microchannel between two parallel plates. Experiments were conducted to investigate the effects of electric double layer (EDL) on flow characteristics with different potassium chloride concentrations in water and with different plate materials, P-type silicon, and glass. Microchannels with a height ranging from 10 ∼ 280 μm were used in the measurement. A mathematical model was developed for steady-state liquid flow with the consideration of EDL effects. The predicted volume flow rates agree well with the measured data. The effects of the EDL field, the ionic concentration, and the channel size on the velocity distribution and friction factor are also discussed in this paper.