In this study, the production of citric acid has been achieved by using Aspergillus niger conidiaspores, entrapped in polyacrylamide gels, and the factors that affect this production have been investigated. On citric acid production the effect of starting sucrose concentration (100-180 g/l), the initial nitrogen concentration (0-0.3 g/l), the effect of the methanol concentration in 100ml feeding medium (0-6 ml), and finally the effect of ethanol concentration (0-6 ml) in 100 ml feeding medium were studied and optimum experimental conditions were determined. As a result of the experiments, the starting nitrogen concentration (0.05 g/l) and the starting sucrose concentration (140 g/l) were optimized and maximum citric acid production was observed for the given conditions. On the other hand, the maximum citric acid production was observed by the addition of 4.0ml methanol and 3.0ml ethanol. (c) 2004 Published by Elsevier Ltd.