Developments in nanotechnology have fostered the widespread use of a diverse array of nanomaterials such as nanosilicas and carbon nanotubes. Nanomaterials are already being used in electronics, sunscreens, cosmetics, and medicines, because they have unique physicochemical properties, such as conductivity, strength, durability, and chemical reactivity. The advent of nanomaterials has also provided extraordinary opportunities for biomedical applications. However, the increasing use of nanomaterials has raised public concern about their potential risks to human health. In particular, recent reports have indicated that carbon nanotubes induce severe inflammation and mesothelioma-like lesions in mice. In this regard, we have attempted to elucidate the pharmacodynamics and safety of nanomaterials in order to develop novel, safe nanomaterials and to establish scientifically based regulations. In this review, we introduce our data on the safety of nanosilicas, particularly the relationships among their physical properties (predominant grain size, configuration, and surface charge), pharmacodynamics, and safety. Our study will help to improve the quality of human life by establishing standards for the safe use of nanomaterials.