The catalyst systems of silver-added vanadia for selective oxidation of cyclopentadiene were studied. As silver of the amount below Ag/V atomic ratio of 0.1 being added into vanadia, the catalytic selectivity for the formation of maleic anhydride was improved. This modifying effect was seemed to be related to the weakening of oxide property of vanadia with the formation of phase AgV₆O₁₅ in vanadium pentoxide. However, the large-amount addition of silver caused the catalyst to lose oxide property, thereby, made the catalytic selectivity poor. Mars and van Krevelen model was applied for kinetics study. The results indicate that the reoxidation of catalyst was the rate determining step and that the addition of silver lowers the activation energy in cyclopentadiene oxidation.