This study involved model evaluation of acute impact of dimethyl phthalate (DMP) on substrate utilization kinetics of aerobic nitrifying activated sludge biomass. A laboratory scale fill/draw reactor acclimated to peptone-meat extract mixture, supplying the biomass, was maintained throughout the study and four sets of batch experiments were conducted to determine the acute impact. After nitrification and carbon removal kinetics of the acclimated biomass were determined as a baseline to the acute inhibitory impact studies, 1g/L DMP concentration was applied. Related experimental data were derived and simulated for model calibration to determine the necessary process kinetics. Model evaluation provided unique information on blockage of nitrification under impact of DMP, and its biological degradation by a fraction of heterotrophic biomass as carbon source at a slower rate than peptone-meat extract mixture.