nanocrystals, named mesocrystal, has been synthesized by a one-step self-assembly crystallization process. [5] Through this novel self-assembly process, magnetic mesocrystals composed of discrete magnetic nanocrystals embedded in an immiscible nonmagnetic matrix have been achieved. [6] However, the embedded nanomagnets inevitably suffer from mismatch strain and defects at the interfaces of two mixed phases, [7] which may produce uncontrollable magnetic property for each nanomagnet and contribute to wide variation of switching field. Thus, magnetic mesocrystals composed of monodisperse well-organized nanocrystals that are not embedded in a matrix have great potential in BPM. Here, we report the fabrication of 2D magnetic CoFe 2 O 4 (CFO) mesocrystal through a combination of nanoseeds layer growth and oxides self-assembly method. The monodisperse CFO nanomagnets protrude from the substrate surface with perfect crystal facets, specific crystallographic orientation, and are fully relaxed. Systematic magnetic characterizations, such as dynamic cantilever magnetometry (DCM) for single CFO nanocrystal, magnetic force microscopy (MFM), and superconducting quantum interference device (SQUID) magnetometer for large area, reveal the novel tilted magnetic anisotropy and the switchable single domain state.A schematic description of the fabrication process is shown in Figure 1a. The nanoseeds layer is prepared based on the different surface energy anisotropy of perovskites and spinels. Most perovskites are characterized by low-energy {100} Bit patterned media exhibits great potential in satisfying the increasing demand for higher information storage density, but the present media fabrication technique is complicated. Here, a 2D magnetic mesocrystal with monodisperse CoFe 2 O 4 (CFO) nanocrystals is fabricated through a combination of nanoseeds layer growth and oxides self-assembly method. The monodisperse CFO nanomagnets protrude from the substrate surface with perfect crystal facets, specific crystallographic orientation, and are fully relaxed. Systematic magnetic characterizations, such as dynamic cantilever magnetometry for single CFO nanocrystal, magnetic force microscopy, and superconducting quantum interference device magnetometry for large area, reveal the novel tilted magnetic anisotropy and the switchable single domain state. This work provides a new way to fabricate bit patterned media with controlled material structure simply by a nanoseeds-mediated self-assembly method.