Graphene oxide (GO) or reduced-GO offer excellent mechanical, electrical and chemical properties. Their nanocomposites have been increasingly explored for attractive applications in diverse fields. However, due to the flexible feature and weak interlayer interactions of GO sheets, flexural mechanical properties of GO-based composites especially for the bulk materials are largely restrained, which would hinder their use in real situations. Here inspired by amorphous/crystalline heterophase features within nacreous platelets, we construct a centimetre-sized GO-based bulk, the building blocks of which consist of crystalline GO and amorphous/crystalline MnO2 phases adhered by polymer-based crosslinkers. The GO/MnO2 heterophase layers are stacked and hot-pressed with further crosslinking between the layers to form bulk artificial nacre. The resultant GO/MnO2-based layered (GML) bulk exhibits the highest flexural strength (up to 203.4 MPa) among all of GO-based bulk materials. Moreover, an excellent fracture toughness, a strong impact resistance and light weight are also achieved. Mechanical and simulation analyses corroborate that the highly ordered heterophase structure together with complex crosslinking interactions across multiscale interfaces, lead to superior mechanical properties. We expect that these results provide interesting insights into the design of structural materials and allow the use of high-performance GO-based bulks in engineering and military applications.