This paper describes the potential of jack bean urease to behave as a catalyst, template and assembling agent by considering its enzymatic activity, steric structure and thermostability, respectively, for the synthesis of 2D structured iron oxide and the 3D hierarchical organization of the 2D structured iron oxide. Maintaining a mixture of JBU, urea and FeCl2 at 60 degrees C for several hours produced Fe3O4 plates; the use of denatured JBU or ammonia instead of JBU yielded spherical particles. Furthermore, the spherical particles synthesized using denatured JBU were akaganeite. These results suggest that JBU acts as both template and catalyst for the synthesis of Fe3O4 plates. In addition, the plates organize into flower-like hierarchical structures as the reaction time is lengthened, which aggregate to form spheres after 48 h. The self-assembly of the plates can be controlled by tuning the denaturation of JBU, which is controlled easily because JBU is thermostable and denatures slowly. The flower-like hierarchical structures possess a relatively high saturation magnetization making them potentially useful in environmental and biomedical applications. (C) 2012 Elsevier Ltd. All rights reserved.