Abstract: Provided are an inactivating agent for enveloped viruses, an inactivating composition for enveloped viruses and a method for inactivating enveloped viruses having high inactivation effects on enveloped viruses even under mild use conditions such as low concentrations or short-time contact. An inactivating agent for enveloped viruses including, as an effective component, (a) an anionic surfactant having a critical micelle concentration of 0.2×10?3 mol/L or more and 2.0×10?3 mol/L or less at 25° C. and a krafft point of 5° C. or less and having a sulfonic acid group, a sulfate group or a salt of these substituents.