We have reported the effect of magneto-ferrite treatment on the growth of excess activated sludge in laboratory scale with extended aeration method. This magneto-ferrite treatment is a new approach for reduction of excess sludge by using ferrite particles and permanent magnets. Two miniature waste water treatment plants were used at the laboratory, one of which was run with magneto-ferrite treatment, whereas other one was run without any treatment. The observations showed good results in the reduction of excess sludge. No evidence of excess sludge was found with magneto-ferrite treatment. The results showed good possibilities of reducing sludge in the arena of biological waste water treatment. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.