Different metal oxide nanostructures can be composited with semiconducting or insulating metal oxides to develop new functionalities, which are very capable for a broad range of applications. Composite metal oxides have a distinct place in nanoscience and nanotechnology because of their extraordinary physiochemical properties. This chapter provides an overview of the recent advancement in the synthesis and characterization of metal oxide-based composite nanostructures. Composite metal oxide nanostructures are applicable in catalysis, sensors, biomedical, and environmental remediation. Composite metal oxides provide a promising way for the development of functional nanostructures. Nanotechnology encourages researchers to develop the modified synthesis of structure-diversified nanostructures and their combined metal–oxide nanostructures.