A semi-submerged biodisk apparatus provided with inert matrix for cell entrapment, previously employed with success for alcohol fermentation, is proposed in this study to overwhelm the well-known problems related to the continuous citric acid production, This immobilized-mycelium system shows at the same time a remarkable increase in citric acid volumetric productivity, with respect to a Continuous Stirred Tank Reactor, but the same progressive activity loss evidenced in the past with comparable immobilized-cell reactors.