Application of microwave energy for materials processing is emerging as an innovative technology with many advantages over the conventional processing, and the rapid progress in this field suggests that microwave material processing (e.g., microwave and microwave-hydrothermal process) will play an outstanding role in the broad field of nanoscience and nanotechnology. This review article gives an up-to-date overview of the current microscopical and physical characterization of the products synthesized by microwave and microwave-hydrothermal process, particularly for oxide nanomaterials because they are indispensable for nanotechnological innovations due to their combinations of infinite variety of structural motifs and properties with manifold morphological features. Basic principles, advantages, and limitations of microwave and microwave-hydrothermal processes are first introduced, and then their recent applications in the synthesis of different classes of functional materials especially for oxide nanomaterials are critically reviewed. Next, the recent progress on the structural and physical characterizations is summarized and discussed. Finally, prospects for future researches within this field are elaborated.