Nanoparticles for biomedical applications have several advantages as multifunctional agents. Among various types of nanoparticles for biomedical applications, silica nanoparticles have characteristic positioning due to their inherent property. The recent development of silica nanoparticles is creating a new trend in nanomedicine. A novel type of silica nanoparticle, organosilica nanoparticle, is both structurally and functionally different from the common (inorgano) silica nanoparticle. The organosilica nanoparticles are inherent organic-inorganic hybrid nanomaterials. The interior and exterior functionalities of organosilica nanoparticles are useful for their multifunctionalization. Biomedical applications of organosilica nanoparticles are leading to a wide range of nanomedical fi elds such as basic biomedical investigations and clinical applications. Multifunctionalizations peculiar to organosilica nanoparticles enable the creation of novel imaging systems and therapeutic applications. In this review, I will introduce differences between (inorgano)silica nanoparticles and organosilica nanoparticles, and then focus on biomedical applications of organosilica nanoparticles toward theranostics.