Abstract: Interferon (IFN)-mediated antiviral signaling pathway is a very important part of fish innate immune response, and interferon regulatory factor 2 (IRF2) can affect fish immunity by regulating the expression of IFN. Therefore, this experiment studied the role of medaka irf2 (Olirf2) in the antiviral signal pathway, which may provide a theoretical basis for antiviral fish through gene editing or genetic modification. In this study, the Olirf2 was cloned, and RNA expression was detected in adult tissues. Moreover, the plasmid pTol2/CMV-IRF2/IE1-pr was constructed by cloning the coding sequence of Olirf2 for eukaryotic expression. In fish cell line FHM, transient expression of Olirf2 promoted the replication of spring viremia of carp virus (SVCV) and reduced the expression of mx1, ifn and irf3 significantly. Further studies by luciferase reporter assay showed that Olirf2 inhibited promoter activities of SVCV-induced NF-κB and ISRE, indicating that Olirf2 may promote the replication of SVCV by inhibiting cellular innate immune response. However, constant overexpression of Olirf2 enhanced the antiviral ability in FHM and increased the expression levels of mx1, ifn and irf3. Therefore, the current research suggested that the Olirf2 has double effect to regulate the antiviral effect based on the duration of expression.