The microstructure studies of the reaction product region (RPR) obtained due to the interaction between the liquid aluminium and polycrystalline zinc oxide substrate at 1273 K has been studied. The RPR extended over the oxide substrate and showed a typical C4 (co-continuous-ceramic-composites) structure composed of two interpenetrating phases. The scanning electron microscopy studies revealed that the large crystals of alumina were surrounded by an Al(Zn) metallic phase. Moreover, the transmission electron microscopy investigation showed the presence of a thin (similar to 250 nm) layer next to the ZnO. The chemical analysis accompanied by the selected area electron diffraction patterns indicated in both cases the same stoichiometric aluminium oxide but of different crystallographic structure, i.e., large crystals had alpha-Al2O3 structure while the layer was identified as metastable delta-Al2O3. The results were compared to those reported for interaction between liquid aluminium and monocrystalline ZnO.