Recoverable degradation of a proton exchange membrane fuel cell (PEMFC) under different relative humidities (RHs) after a whole night rest was investigated. A single cell was operated under drive cycle to simulate the working conditions of fuel cell vehicle. It was found that the cell performance decreased after 5 h operation and recovered mostly after one night rest at higher humidities, i.e. 100%, 75% and 50% RH for both cathode and anode sides; while continuous decrease took place at lower humidity, 35%RH. Polarization curve, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted before and after every 5 h drive cycle for investigating the mechanism of the recoverable degradation. It was found that water content, current density and thermal management might be the main contributions to the performance degradation, by impacting the membrane conductivity, internal resistance, electrode kinetics, and catalyst utilization. A good understanding of voltage recovery phenomenon after several hours rest and its effect on durability will be helpful in improving the reliability and durability of PEMFC. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.