Production and consumption of confectionery products, such as chocolate, sugar, and cookies, have increased worldwide. Thus, management and treatment of confectionery effluents, as one of the most important agro-industrial wastewaters, become essential. Confectionery industries produce high-strength and highly biodegradable wastewaters that are appropriate for biological treatment prior to discharge. In this study, long-term dynamic performance of a full-scale anaerobic expanded granular sludge bed (EGSB) reactor treating confectionery effluent was simulated by using Anaerobic Digestion Model No. 1 (ADM1). Substrate fractionation was carried out based on the ADM1 state variables, and then, the model was calibrated with 300 days of operation data. The calibrated model could capture the dynamic performance of the anaerobic reactor for a long validation period of 500 days. Although the reactor was operated under highly fluctuating volumetric loading rates (VLR) between 0.2 and 5 kg chemical oxygen demand (COD)/m(3) day, the model results indicated medium to high prediction accuracy for effluent COD, methane generation, total volatile fatty acids (VFA), and pH parameters. Mean relative absolute errors for COD, methane flow, VFA, and pH parameter simulations were 22%, 16%, 29%, and 1%, respectively. The study presents the applicability of ADM1 for full-scale reactors treating industrial wastewaters.