A previously developed model for sequencing batch reactors was used in this study to investigate the effect of some of the model stoichiometric and operating parameters on the performance of the system. With regard to the effluent chemical oxygen demand (COD) concentration, the model predictions were determined to be correct for the parameters Y-p,f(p) and S-sf. However, the stoichiometric parameters alpha, Y-h and the operating parameter X-ao were determined to have significant effect on the effluent COD concentrations. The intermediate COD concentrations are affected by the parameters Y-p, Y-h, S-sf and X-ao. To use the model for design or control purposes, special attention should be given to the parameters that affect the effluent COD concentration.