Effect of channel-to-rib width ratio of flowfield plates on micro proton exchange membrane fuel cell stacks performance test (VI/PI) was studied experimentally in the present study (see Fig. 1). The channel-to-rib width ratio was varied from 0.5 to 2. The optimum channel-to-rib width ratio of flowfield plates for micro PEM fuel cell stack was found. Moreover, the pressure drop in flowfield on both anode and cathode was measured and, with aid of pressure drop obtained for H2/air delivery, an optimal channel-to-rib width ratio in terms of the net stack power gain factor (= stack power gain/stack power consumption) of 0.67 can be also obtained for the present study.