Poly(methacrylic acid)(PMAA) coated magnetite (Fe3O4) nanoparticles were synthesized via co-precipitation in aqueous solution with the use of conventional magnetic stirring and ultrasonic agitation. It has been shown that the ultrasonic agitation during the synthesis of magnetite particles decreased the size of PMAA-coated magnetic agglomerates significantly. The primary particle size of iron oxide particles was determined as approximately 10 nm by X-ray diffraction method (Scherer's equation). The volume weighted mean size (D [4,3]) of PMAA coated magnetite particles was determined as about 80 nm using laser diffraction technique. (c) 2013 Elsevier Ltd. All rights reserved.