Magnetic Janus particles consisting of iron oxide particles and polystyrene: were prepared by miniemulsion polymerization and subsequent seed emulsion polymerization. The polystyrene areas on the Janus particle surface were then functionalized by grafting poly(acrylic acid) (PAA) brushes via photo emulsion polymerization or by coating palladium, nanopartieles via a vapor deposition method. The magnetic Janus particles partially grafted with PAA were pH sensitive and able to immobilize proteins. The orientation of Janus particles pattially covered with, palladium in the wax water interface could be controlled by an external magnetic force. These functional magnetic Janus particles with superparamagnetism have potential, applications in, e.g., controlled, interfacial catalysis triggered by a magnetic force.