The output performance of polymer electrolyte fuel cell is affected by water droplets. In order to examine the two-phase gas-liquid flow in gas channels and to know its influence on output performance, cell voltage and local differential pressure in cathode gas channels were measured simultaneously, and the influence of local liquid water distribution on cell voltage was examined on various operating conditions. As a result, it was found that the degradation of voltage and its stability were affected by droplets in channels, and these phenomena were different by the place where there was a droplet. Furthermore, the movement and the flow condition of liquid water in gns channels were examined by experimental results and relative humidity distribution calculated by a numerical analysis. As a rest It, it was possible to estimate the two-phase flow model by apparent relative humidity including liquid phase.