Over the last 10 years, the antiviral and antimicrobial activities of non-functionalised inorganic nanoparticles against different pathogens were experimentally shown. This effect has attracted the attention of scientists due to the COVID-19 pandemic; however, its mechanism is still unclear. For understanding the mechanism of nanoparticle’s action, it is important to know how this action depends on the parameters of nanoparticles and the properties of a pathogen. In the work, we have studied the action of gold nanoparticles on the viruses outside and inside the cell and compared this action with two sizes of nanoparticles and two types of viruses. The study has been conducted for adenovirus and H1N1 influenza virus, and gold nanoparticles of 5 nm and 20 nm diameter. Virucidal and antiviral actions were observed experimentally for both sizes of nanoparticles against both viruses. It has also been shown with the electron microscopy that the viruses may be destructed in 2 h after adsorption of 5 nm gold nanoparticles on their surface; and that the viruses may change their shape in 2 h after adsorption of 20 nm nanoparticles on their surface. The model of physical adsorption of nanoparticles on the virus surface due to near-field interaction was used to explain observed results.