Significance The human respiratory syncytial virus (RSV) is a significant cause of lower respiratory tract infections in the young and the elderly and a substantial burden to global human health. Currently, there are no specific and effective treatments for RSV infections. Here we report the first X-ray crystal structure of RSV nonstructural protein 2 (NS2), which revealed a unique fold. The combined biochemical and structural analyses of the NS2 structure identified a region that binds to and inhibits ubiquitination of an inactive form of RIG-I and MDA5, preventing downstream signaling and type I interferon production. Our study provides structural insight into the mechanism of how NS2 antagonizes IFN response to RSV infection and defines a target for antiviral development.