Hybrid nanostructures of low-dimensional metal oxide (MO) semiconductors based on two-dimensional (2D) graphene nanosheets have been considered as one of the most promising nanomaterials for extensive applications. Unfortunately, it is still challenging to rationally design and fabricate MO/graphene hybrids with highly controllable nanostructures and desirable properties, which are of paramount importance for practical applications. Here, we report a novel, facile and “green” glycerol-mediated self-assembly method, using α-Fe2O3 semiconductor as an illustrative example, for the controlled growth of MO with a well-defined nanostructure on 2D graphene nanosheets. Based on this new method, we first demonstrate the ability to exquisitely tune the α-Fe2O3 nanostructure from zero-dimensional quantum dots (~3.2 nm) to one-dimensional mesoporous nanorods, and eventually to 2D mesoporous nanosheets over the entire surface of graphene nanosheets. A possible formation mechanism has been proposed based on the systematic investigation of the morphological evolution and growth processes of α-Fe2O3 on graphene. The as-synthesized samples exhibit excellent performance for photo-Fenton treatment of polluted water at neutral pH under visible light irradiation. Moreover, TiO2 and Fe3O4 quantum dots (~5.2 and 3.3 nm, respectively) ultradispersed on graphene are also successfully synthesized by this method, demonstrating the versatility of this method for rational fabrication of novel MO/graphene hybrids with huge potential applications.