Abstract: A process for producing butadiene from a monoolefin having 4 carbon atoms by a vapor-phase catalytic oxidation reaction in a fluidized bed reactor, including a first step of producing the butadiene by bringing the monoolefin having 4 carbon atoms into contact with a catalyst and a second step of removing a part of the catalyst from the fluidized bed reactor while the vapor-phase catalytic oxidation reaction is proceeding, regenerating the catalyst removed, and feeding the regenerated catalyst to the fluidized bed reactor while the vapor-phase catalytic oxidation reaction is proceeding, wherein a ratio of an amount (kg/hr) of the regenerated catalyst fed to an amount (kg/hr) of the monoolefin having 4 carbon atoms fed is 0.3% or more.