Abstract: A PEMFC was designed and fabricated with the microelectromechanical system （MEMS） technology. The anode has a pin-serpentine-combined flew field and the cathode has two layers with small channels flew field for air-breathing. The pore size of small channels near the MEA ranges from 5 m to 50 m. This paper focuses on the effects of relative humidity and temperature on fuel cell performance. Results show that PEMFCs with 11 m and 15 m micro-pore in cathodes performs well at 20℃ and 30-70%RH. When air humidity is controlled at 50%RH, the peak power （Pmax） of PEMFC with 11 m micro-pore in cathode went up by 14.9% when temperature rose from 10℃ to 40℃. In contrast, when doing the same thing without air humidity control, Pmax first increased to the maximum at 20℃ and then decreased.