This study explores the use of mathematical modeling to evaluate the performance of conventional activated sludge systems at wastewater treatment plants (WWTPs). With expanding objectives and increasingly strict regulations, mathematical modeling provides a valuable tool for evaluating WWTP performance. The research focuses on Gamasa WWTP located in the Dakahlia governorate. Historical data, design reports, and additional analyses were collected through site visits and a comprehensive sampling campaign. The wastewater was characterized, and the plant-wide model was calibrated following the protocol of Dutch Foundation of Applied Water Research STOWA. Sensitivity analysis is done to identify the most important kinetic and stoichiometric parameters to be adjusted during the calibration process. The most sensitive parameters were aerobic yield, anoxic yield, ordinary heterotrophic maximum specific growth rate, ordinary heterotrophic substrate half saturation, ordinary heterotrophic aerobic decay rate, soluble unbiodegradable COD, COD: VSS ratio, endogenous residue COD: VSS ratio, non-colloidal slowly biodegradable COD, ammonia oxidizing bacteria maximum specific growth rate, ammonia to total kjheldahl nitrogen fraction, ammonification, soluble unbiodegradable TKN, aerobic yield, N in biomass, ammonia oxidizing bacteria substrate half saturation, ammonia oxidizing bacteria aerobic decay rate, nitrite oxidizing bacteria maximum specific growth rate and aerobic yield, and phosphate to total phosphorus fraction. Model's validity was assessed using different validation periods, with average relative deviation (ARD) values below 20% considered acceptable. Overall, this study demonstrates the effectiveness of mathematical modeling in evaluating performance of current WWTPs and developing a mathematical model which can be used for improvement of WWTP to meet stringent wastewater treatment regulations.