Up till now there is no information available on if and how NSDV/GV manipulates the host innate immune system. Because of the difficulties in handling CCHFV, there is only limited correlation of studies on virus and on viral proteins. We provide here the evidence that NSDV/GV is able to inhibit IFN induction as well as IFN action. We could identify the viral L protein as being responsible for these inhibitory effects. Furthermore NSDV is able to reduce total protein ubiquitination and ISG15ylation in infected cells. This deconjugating activity, as with CCHFV, is located in the N-terminal part of the NSDV L protein containing the OTU domain. Inactivation of the OTU enzymatic activity resulted in loss of its ability to antagonise IFN responses.