In this study, a serial electrochemical hydrogen compressor (EHC) stack was designed to compress hydrogen gas to hundreds of bars. The operating parameters were examined to analyze optimal performance. First, a serial stack was designed to enable the EHC to operate at pressures exceeding hundreds of bars. The circular design of the stack was chosen specifically to prevent hydrogen leakage. A 127μmthick membrane was selected owing to its relatively good pressure resistance and performance. Through a serial EHC stack of 3 cells, hydrogen was pressurized over 120 bar. A parametric study showed that the pressure-ratio across the membrane barely affected the performance. Additionally, the higher the temperature and relative humidity, the better the performance. By increasing the temperature to 70 °C, the power consumption was reduced by 40 %. At 100 % relative humidity, the EHC exhibited the lowest power consumption. Finally, the performance of the serial stack was analyzed under optimal operating conditions, wherein it demonstrated an efficiency over 64 % for below 0.03 kg/day mass-flow rate of compressed hydrogen. However, efficiency decreased to 12 % at a mass-flow rate over 0.17 kg/day.