Citric acid production using immobilised Aspergillus niger was studied. For the immobilisation, Viscopearl (porous cellulose beads) was used as the carrier. The immobilised ratio of the biomass to the carrier was controlled by changing the preculture periods. It significantly affected the production rate, the yield and the maximum concentration of citric acid. The optimum value of the preculture periods was 3 days in relation to the citric acid production. The initial sugar concentration also affected the citric acid production, and the optimum value was 100 g dm(-3). Furthermore, the repeated batch culture was carried out using the immobilised biomass at several batch intervals. The optimum values of the batch interval were 6 days for the citric acid productivity and 8 days for the most cost effective process.