Magnetorheological (MR) fluids have been successfully utilized in versatile fields but are still limited by their relatively inferior long-term dispersion stability. Herein, bio-inspired passion fruit-like Fe3O4@C nanospheres were fabricated via a simple hydrothermal and calcination approach to tackle the settling challenge. The unique structures provide sufficient active interfaces for the penetration of carrier mediums, leading to preferable wettability between particles and medium oils. Compared with the bare Fe3O4 nanoparticle suspension, the resulting Fe3O4@C nanosphere-based MR fluid exhibits desirable stability and relatively low field-off viscosity even at a high particle concentration up to 35 vol %.