Activated sludge process is widely used for wastewater treatment throughout the world with various modifications. The aim of this research was to study the effect of using effective microorganisms (EM) to enhance the activated sludge process. A model has been constructed to simulate activated sludge process. It consisted of two reactors (EM-dosed and control) operated simultaneously. The results of the present study showed that the reactor induced with EM achieved removal ratios of 84.5%, 91.5% and 96.0% in TSS, COD and BOD respectively compared to 63.5%, 66.0% and 74.0% in the control reactor. Increasing EM dose from (1/7500) to (1/1000), increasing COD and BOD removal ratios from 71.0%, 75.5% to 91.5%, 96.0% respectively compared to 68.0%, 74.0% in the control reactor . Also results indicated that the pulse dose addition method achieved higher efficiency in early days (7 days), 90.0% and 94.5% for COD and BOD respectively compared to 78.0%, 82.5% in daily dose method. However, the daily EM dose method showed higher removal efficiency at the long run application (one month) 92.0%, 85.7% for COD and BOD respectively compared to 82.5%, 76.0% in pulse dose method. EM dose (1/1000) showed significant higher removal ratios at lower hydraulic retention time (HRT=4 hours), where the EM reactor achieved removal efficiency for COD and BOD were 84.5% and 91.5% respectively compared to 63.0%, 68.5% at the control reactor. Enzymes evaluation showed that the enzymatic activity of EM has more ability in the oxidation of organic materials than of bacteria found in the control reactor.