Citric pulp bran was used for the first time as substrate for phytase synthesis under solid-state fermentation. An A. niger FS3 phytase strain was applied in optimization studies. A Plackett-Burman screening design identified significant physicochemical variables. These preselected variables were subsequently optimized using a central composite rotational design (CCRD). The maximum phytase production was achieved with the following optimum variables: 30 degrees C temperature, 65% initial moisture content, 0.3M Na-citrate buffer concentration, initial pH 5.0, and 1.5% urea concentration. An overall 4.3-fold improvement in phytase production was successfully achieved.