The electrical and mechanical properties of new lightweight graphite polymeric separator plates aged in a PEM fuel cell were investigated to assess their resistance to short-term durability. While the changes in electrical properties of great interest to the operation of the fuel cell, mechanical and dimensional stability over the life of the cell are critical. Thus, new polymeric based separator plates developed at Virginia Tech were aged under standard operating conditions in a PEM fuel cell over 300 hours at low pressure and 85°C. A comparison of conductivity, stiffness and strength of aged plates was made to as manufactured and unaged plates. Over the aging period, electrical conductivity did not decline even as the fuel cell performance showed some changes as evidenced by polarization curves. However, the mechanical strength of the monopolar plates was observed to declined less than 10% after 300 hours of fuel cell operation, due to the lack of stability of the polyester resin used to facilitate the rapid manufacturing of these new plates. These property changes were found to be independent of aging on the reduction and oxidation sides. Further work continues on plates formed through both fiber wet lay technology and those produced by compression molding of unique graphite filled epoxy systems, and to improve the electrochemical performance of cells fabricated using the resulting plates to levels comparable to those observed when using existing plate materials.