High fidelity and regularity structures of nanoscale materials has opened up new opportunities for developing miniaturized devices. A simple yet robust approach of magnetic field assisted controlled evaporative self-assembly (CESA) is developed to achieve Fe 3 O 4 nanoparticle (NP) micro-and nanopatterns in a two dimensional (2D) direction. In the magnetic field assisted CESA process, the selfassembly morphology can be well controlled by varying extrinsic and intrinsic variables such as temperature, external magnetic field, and concentration of Fe 3 O 4 NPs. Under the optimized magnetic field rotation frequency and temperature, 2D self-assembly of Fe 3 O 4 NPs can be well realized. In addition, as photoactive sites, double bonds on the surface of Fe 3 O 4 NPs allow the growth of polymer brushes by self-initiated photografting and photopolymerization (SIPGP), and the further achievement of free-standing magnetic composite films with well-defined patterns. † Electronic supplementary information (ESI) available: The SEM, optical, AFM images of Fe 3 O 4 nanoparticles, Fe 3 O 4 nanoparticles patterns and free-standing lm. See