Box-Behnken experimental design method was used to optimize the experimental conditions of photocatalytic removal of ammonia from synthetic wastewater by ZnO/Oak charcoal photocatalyst. The hybrid photocatalyst was synthesized by impregnation method and characterized by XRD, FTIR and FESEM analyses. The results of analyses showed the suitable dispersion of ZnO over the support surface. Also, the FESEM analysis confirmed the good features of the Oak charcoal as either support or adsorbent. pH (4-12), catalyst dosage (0.5-2 g/L) and initial ammonia concentration (85-850 mg/L) were the main parameters affecting the ammonia removal. The results of experiments were modeled by a second-order polynomial equation. The high value of the determination coefficient (R-2 = 99.6 and adjusted R-2 = 98.9%) revealed that the experimental data fitted well with the proposed model. The maximum efficiency of ammonia removal was obtained about 80% at optimum conditions of initial ammonia concentration of 153.9 mg/L, catalyst dosage of 1.59 g/L and solution pH 10.5. Based on the results of analysis of variance, the significance order of the independent parameters was as follows: initial ammonia concentration > catalyst dosage > solution pH. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.