Three-dimensional (3D) flowerlike hierarchical Fe3O4@Bi2O3 core–shell architectures were synthesized by a simple and direct solvothermal route without any linker shell. The results indicated that the size of the 3D flowerlike hierarchical microspheres was about 420 nm and the shell was composed of several nanosheets with a thickness of 4–10 nm and a width of 100–140 nm. The saturation magnetization of the superparamagnetic composite microspheres was about 41 emu g−1 at room temperature. Moreover, the Fe3O4@Bi2O3 composite microspheres showed much higher (7–10 times) photocatalytic activity than commercial Bi2O3 particles under visible-light irradiation. The possible formation mechanism was proposed for Ostwald ripening and the self-assembled process. This novel composite material may have potential applications in water treatment, degradation of dye pollutants, and environmental cleaning, for example.