Using engineered bacteria as therapeutic agents against tumors is one of the state-of-the-art techniques emerging with the development of synthetic biology.Although it has great potential in cancer treatments, one major challenge is how to precisely target the engineered bacteria to the tumor and constrain the bacteria within the tumor, in order to minimize side-effects to the body.In this study, we constructed a synthetic magnetic bacterium with magnetic nanoparticles immobilized on the outer membrane of Escherichia coli through stable interaction between GFP and its corresponding antibody.This study enables us to develop a novel gene/drug delivery system, and provides us an additional option in biomedical application developments.