Recently, a variety of nanoparticles have been considered as an attractive way that is effective and helpful in diagnosis and treatment of cancer and diseases through development in nanoscience and nanotechnology. Nanoparticles refer to tiny particles between 100 nm and 1 μm. The objective of this paper is to review the current applications, the research trend, and the possibility in future of the metallic nanoparticles in drug delivery, imaging, therapy, and combined imaging and therapy, as well as hearing research. The nanoparticles for effective drug delivery have been used to selectively target and kill the cancer cells or tumor cells and to transport molecules, nanoparticles, and cells into solid tumors in chemotherapy and radiation. The nanoparticles in hearing research have been used to prevent or treat the noise-, ototoxicity-, inflammatory-, viral-, and immune-mediated hearing loss and cell death processes using genetic and trophic factors enhancing repair processes of hair cell in the cochlea. The nanoparticles for effective imaging have been used to confirm a detailed view of targeting in live cells and their interactions with intracellular molecules and as contrast agents for CT, MRI, and x-ray imaging. The nanoparticles in therapy have been used in chemotherapy, immunotherapy, radiotherapy, thermotherapy, and photodynamic therapy by targeting the fast growing cells, blocking some critical elements of the cell division process, transporting various compositions, and increasing the dose and effectiveness of x-rays. Recently, the nanoparticles have been used to increase the effectiveness of individual modality image or therapy by combining noninvasive multimodality imaging and molecular therapy. This method can provide a new insight and intuition on the diagnosis and treatment of the various cancers and diseases including hearing loss.