For use in a fuel cell separator comprising a separator substrate, a primer layer, and an elastomeric seal, a sealing material comprises a primer composition containing Si—H groups of which the primer layer is formed, and a liquid addition-curable silicone rubber composition containing alkenyl groups and Si—H groups of which the elastomeric seal is formed. A molar ratio of the total amount of Si—H groups to the total amount of alkenyl groups per unit weight of the primer composition and the silicone rubber composition is in the range: 5.0