In this study, effect of magnetic field on the activity of activated sludge in wastewater treatment was investigated. During the experiment, biodegradation duration, magnetic density, operating temperature and medium pH value were changed within the ranges from 0 to 60 h, 0 to 500.0 mT, 10.0 to 50.0 degrees C and 3.0 to 12.0, respectively. These results revealed that activated sludge acclimatization and organic pollutant biodegradation processes under magnetic field were stimulated, resulting in a higher efficiency of wastewater treatment. Biodegradation of organic compounds under magnetic field could reach stable states after 48 h. The organic compounds removal rate first roared up and then fell down with the increase of magnetic density of the field, turning at 20.0 mT. On account of application of magnetic field, the range of temperature and pH, which is suitable for the growth of microbe, were 20.0-40.0 degrees C and 6.0-10.0, respectively, which were expanded compared with those without the magnetic field. (C) 2010 Elsevier Ltd. All rights reserved.