A central composite design (CCD) was used to optimize fermentation condition for the production of citric acid by Aspergillus niger NRRL 567 using wheat straw. The statistical model was capable of predicting optimum condition for maximum citric acid production. The pH of nutrient solution, inoculum density and moisture content were found to significantly affect citric acid production, while fermentation temperature was showed insignificant effect within tested range. The maximum citric acid production of 123 g/kg dry wheat straw (DWS) was predicted with the fermentation condition of 35!, pH 8, 3.74 x 10⁶ spores/ml and 80% moisture content at 72 h. Maximum citric acid production on optimized condition represented a 1.6-fold increase compared to that obtained from control experiment. The experimental data fitted well with the model predicted values and the CCD has proved to be very effective for the optimization of the citric acid production.