Temperature distribution in the through-plane direction in polymer electrolyte fuel cell (PEFC) is key information to achieve proper water management. We fabricated an in-line thermocouple of 49 μm diameter, insulated by Parylene coating with 12 μm thickness. The supporter for the thermocouple was fabricated to position the thermocouple to an exact measurement-point in cell, and to protect the thermocouples from the damage during assembling and operating the cell. Seven in-line thermocouples were placed in the cell in array. It was found that the insertion of thermocouples did not cause large decrease of the cell performance. When the current of 0.3 A/cm2 was loaded under the condition of 60 °C separator temperature with supplying H2/Air humidified at 80 % RH, the cathode catalyst layer temperature showed the increase of 1.9 °C and the maximum in the cell.