Efficient cold start of PEFC under freezing point can be realized by keeping the super-cooled state of generated water. If a super-cooled state is maintained, the cell can start under a freezing point with generated heat, and the cell reaches a steady state without the gas-supply block caused by the ice from the generated water. Difficult task, such as a shorter cold-start at a lower temperature, is possible by adequate choice of component material used in the cell, and by active heat generation with a suppressed air supply. Against such a background, this paper discussed which characteristic of the component in cell leads to the success of cold start, namely of keeping super-cooled state during cold start. This analysis was performed on the basis of heterogeneous nucleation theory, which considers the wettability of surface of the component material.