The effects of the environmental conditions and the channel depth for an air-breathing polymer electrolyte membrane fuel cell were investigated experimentally. The fuel cell used in this work included a membrane and electrode assembly, which possessed an active area of 25cm2 with Nafion 117 membrane. Triple serpentine designs for the flow fields with two different flow depths were used in this research. The experimental results indicated that the relative humidity and temperature play an important role with respect to fuel cell performance. The fuel cell needs to be operated at least 20 min to obtain stable performance. When the shallow flow field was used, the performance increased dramatically for low humidity and slightly for high humidity. The current density was obtained around only 120mA/cm2 at 30C with an 80% relative humidity, which was nearly double the performance for the deep flow field. The minimum operating temperature for an air-breathing fuel cell would be 20C. When it was 10C at 60% relative humidity, the open circuit voltage dropped to around 0.65 V. The fuel cell performance improved with increasing relative humidity from 80% to 100% at high current density.