Abstract: Composite core/shell Fe₃O₄@mSiO₂ nanoparticles are synthesized by coating mesoporous silica onto a submicrometer-sized Fe₃O₄ spheres. A Janus silica cage was synthesized by selectively grafting a hydrophilic polymer amine ended PEG-NH₂ containing folic acid (FA) and pH responsive polymer of poly(2-diethylaminoethyl methacrylate) (PDEAEMA) onto the exterior and interior sides of the mesoporous SiO₂ shell. The chemical composition and microstructure of Janus cages were studied by SEM, TEM, XRD, FT-IR, UV-Vis and TGA. The results showed that the prepared Janus cage had a clear chemical partition and the paramagnetic core inside the cavity was responsible for magnetic collection. Oil-soluble substances can be collected in pH responsive Janus cages at pH higher than 7.2, and controlled release can be achieved at pH lower than 7.2. Furthermore, doxorubicin (DOX) was selected as a model drug, and the performance as a responsive drug carrier for loading and controlling release of oil-soluble drugs were investigated. The results showed that Janus cages loaded with drugs could achieve responsive drug release in a simulated tumor pH environment. It has good application potential in the field of targeted drug delivery and responsive release.