Temperature and voltage distribution in membrane electrode assembly (MEA) significantly impact the performance of fuel cells. However, conventional sensors fail to evaluate inner data with accuracy owing to their enormous size and limitation of conducting only an external measurement in fuel cells or cm-scale sensors for invasive measurements. Based on micro-electro-mechanical systems (MEMS) technology, this work integrates a micro temperature and voltage sensor on parylene, which is used as a flexible substrate. The micro sensors are then embedded in upstream, midstream and downstream for MEA monitoring, in which the temperature and voltage vary during operations. Experimental results indicate that the in-situ temperature and voltage exceed the ex situ ones. Moreover, in addition to the temperatures in the upstream and midstream surpassing those in the downstream, voltages in the upstream and midstream are lower than those in the downstream. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.