Graphene with a large area was synthesized on Cu foils by chemical vapor deposition under ambient pressure. A 4″ × 4″ graphene film was transferred onto a 6″ Si wafer with a thermally grown oxide film. Raman mapping indicates monolayer graphene dominates the transferred graphene film. Gas sensors were fabricated on a 4 mm × 3 mm size graphene film with a 1 nm palladium film deposited for hydrogen detection. Hydrogen in air with concentrations in 0.0025-1% (25-10,000 ppm) was used to test graphene-based gas sensors. The gas sensors based on palladium-decorated graphene films show high sensitivity, fast response and recovery, and can be used with multiple cycles. The mechanism of hydrogen detection is also discussed. © 2010 Published by Elsevier B.V.