The selective hydrogenation of cyclopentadiene to cyclopentene has been studied in the liquid phase using Pd and Pd-Me/Al2O3 bimetallic catalysts (Me = Mn, Ni, Co, W). The highest activity was obtained with Pd-Co and Pd-W/Al2O3. For these catalysts, no hydrogen or CO chemisorption was detected although Pd could be seen by XPS at 335.8 eV; it is considered that new species, more active for the selective hydrogenation of cyclopentadiene, appeared at the catalyst surface. The sulfur resistance towards thiophene has also been studied. It was observed that the highest sulfur resistance is coincident with the highest activity. XPS analysis shows that the poisoning species is thiophene adsorbed on the catalyst surface.