An immunomagnetic composition, a preparation method and a use thereof, and a kit for treating a cancer. The immunomagnetic composition comprises a core layer, a shell layer and an outer layer. The shell layer is composed of a composite and encapsulates the core layer. The composite is formed by the combination of fucoidan, oxidized dextran, and a plurality of superparamagnetic iron oxide nanoparticles by hydrophobic interaction. The outer layer comprises at least one antibody.
