Thermal and electrochemical durability of carbonaceous composite plates, which are made from graphite powders and a resin for use as bipolar plates of PEMFC (proton exchange membrane fuel cell), were investigated. The thermal durability was investigated by TG (thermal gravimetry) coupled with DTA (differential thermal analysis) technique under air up to 600 degrees C. A weight loss was significant over 300 degrees C, but the hydrophobicity was decreased after heated at 80 degrees C for 192 h. The electrochemical durability was investigated in 10 mu mol dm(-3) of hydrochloric acid solution under nitrogen or oxygen atmosphere by means of potential holding test from 0.8 to 1.5 V against RHE (reversible hydrogen electrode) at 80 degrees C. During the potential holding tests, CO2 production due to the corrosion was quantified by a GC (gas-chromatography) and the production was detectable above 1.3 V irrespective with atmosphere: on the other hand, it was clarified from the contact angle measurements that the hydrophobicity was changed below 1.3 V. The results of this study showed that the carbonaceous composite plates were electrochemically degraded under PEMFC condition and were seriously degraded in URFC (unitized regenerative fuel cell) condition. (C) 2010 Elsevier B.V. All rights reserved.