Thin metallic bipolar plate (BPP), due to mechanical strength, thermal conductivity, high power density, and relatively low cost, is considered to be an alternative to graphite BPP in proton exchange membrane (PEM) fuel cell. However, shape error of thin metallic BPPs is not avoidable due to its flexibility and springback in stamping process, as well as deformation resulted from thermal stress in welding process. In this study, fluctuation analysis is conducted and response surface methodology (RSM) is adopted to establish the relationship between shape error and contact pressure distribution on gas diffusion layer (GDL). Thin metallic BPPs made of stainless steel (SS) 304 sheets are fabricated and shape error is defined. Two types of specimens are selected and assembled with GDL. Effects of assembly force, BPP size and shape error are systematically investigated and a response surface model is developed to predict the effect on contact pressure distribution resulted from the shape error of BPP. The methodology in this study is beneficial to understand the effect of the shape error and predict the acceptable shape error. Based on the model, tolerance of the shape error of BPP is given to guide the manufacturing process of the thin metallic BPP. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.