Provided is a method of preserving a PEFC stack, which is capable of controlling degradation of performance of the PEFC stack during a time period that elapses from when the stack is placed in an uninstalled state until it is placed in an installation position and is practically used. Provided is a preservation assembly of the PEFC stack which is capable of sufficiently inhibiting degradation of performance of the PEFC stack particularly during a time period that elapses from when the stack is placed in the uninstalled state until it is placed in the installation position and is practically used. A method of preserving a PEFC stack that is provided with an oxidizing agent passage (30) having an inlet and an outlet and extending through a cathode and a reducing agent passage (40) having an inlet and an outlet and extending through an anode, comprising preserving the PEFC (200) stack in an uninstalled state in such a manner that an interior of the oxidizing agent passage (30) and an interior of the reducing agent passage (40) are set in a pressure-reduced state.