Disposal of chemical and toxic pollutants via industrial wastewaters into the environment has always been a hazard to water resources. According to scientific reports, biological systems are the most suitable method for treatment of such wastewaters. Obviously various effective organisms depend on the type of pollutants, treatment plant system and environmental conditions. Identification of the most effective microorganism is necessary for determination of optimum conditions, method of control and monitoring of bioreactor to access the maximum efficiency and improvement of operation. The objective of this study was to identify PHENOL degrader aerobe bacteria in combined biological PHENOL-treatment system of biofilter and activated sludge. Some amount of biological sludge was provided from domestic wastewater treatment as a primary source of microbe and was added to the designed reactor. Then samples were collected after growth of microbial mass. PHENOL concentration and environmental condition (i.e. dissolved oxygen and pH) were stabilized after gradually adaptation of the system to PHENOL All samples were collected by sterile glass container. These samples were cultured on enrichment media and identified by various differential tests. dentification results proved PHENOL degrader bacteria are aerobe, nonfrementer but had negative result for of test with glucose as substra. These isolated bacteria were Pseudomonas aerginosa, P.alcaligenes, Moraxella sp, Acinetobacter sp, and Brevundiomonas vesicularis Because PHENOL was the only substrate and nitrogen and phosphorus as necessary factor in this system, all biodegrader bacteria used only PHENOL as their both carbon and energy source. PHENOL is degraded in a completely aerobic condition and dissolved oxygen concentration is sufficient since all the bacteria are aerobes.