Fe3O4/polymer hybrid microcapsules were prepared via a template-free route which is based on polyamine-salt aggregates (PSAs) self-assembly approach. The measurements of transmission electron microscopy (TEM) indicated that the diameter and shell thickness of the microcapsules could be tuned by varying the experimental conditions, such as the concentration of reactants and evolution time employed during the PSA assembly. The results of vibrating sample magnetometer (VSM) demonstrated that the magnetic nanoparticles content of the synthesized microcapsules was tunable and all samples exhibited superparamagnetic behavior. After filling appropriate perfluorocarbon into the inner cavities of the microcapsules, the biomedical applications of the resultant microbubbles, including ultrasonic imaging (USI) and magnetic resonance imaging (MRI), were studied in vitro. It showed that the synthesized magnetic microbubbles possessed both strong ultrasound contrast enhancement capability and high relaxation rate. The excellent acoustic and magnetic properties of these self-assembled microbubbles ensure that the Fe3O4/polymer hybrid microbubbles have great potential as MRI/USI dual modality contrast agents. (C) 2016 Elsevier Inc. All rights reserved.