An air-breathing microfluidic fuel cell with a cylinder anode was proposed and tested in acidic and  alkaline electrolytes. In acidic condition, the CO2 bubbles were partly constrained blow the spacer, but would cover the anode surface area and  block  the fuel transport. Electrochemical Impedance  Spectroscopy (EIS) measurement also revealed that the gas column can increase the inner ohmic  resistance by reducing the proton conduction.  Spontaneous bubble removal was observed but this process was highly random. On the contrary, non-bubble was observed in the alkaline electrolyte,  therefore much higher and more stable cell  performance was obtained. In addition, the  performance  characteristics of the presented  cell in alkaline condition were studied.