Abstract: The purpose of this study is to investigate the effect of Reduning injection (RI) on influenza A virus (IAV) and its mechanism. We evaluated the cytotoxicity of RI in A549 and MDCK cells by cell counting kit-8 (CCK-8) assay. Western blot and cytopathic effect (CPE) assays were applied to test the effects of RI on viral protein, CPE and virus virulence to evaluate its inhibitory effect. The proteins level of heme oxygenase 1 (HO-1), nuclear factor erythroid 2-related factor 2 (Nrf2), phosphorylation of P38 mitogen-activated protein kinases (MAPK) and extracellular signal-regulated kinases 1/2 (ERK1/2) were detected by Western blot. Real-time fluorescence quantitative PCR (qRT-PCR) was used to detect the RNA expression of interferon-α/β (IFN-α/β). The relative luciferase reporter assay was used to analyze the promoter activity and transcriptional regulation of Nrf2. The results indicated that RI inhibited IAV-induced MDCK cytopathies in a dose-dependent manner, decreased M2 protein of influenza virus and viral titer, indicating that it has definite effect on inhibiting IAV. RI promotes the phosphorylation of P38 MAPK and ERK1/2, activates the activity of Nrf2 nuclear transcription factor, increases the expression of Nrf2 protein in the nucleus, thus up-regulates the expression of HO-1 protein, and ultimately increases the IFN-α/β mRNA level. In summary, our results demonstrated that RI inhibits the replication of IAV by activating MAPK/Nrf2/HO-1 signaling pathway, revealing a new mechanism of RI against influenza virus, and providing theoretical basis for clinical treatment of influenza virus.