Protective effects of recombinant human granulocyte macrophage colony stimulating factor (rHuGM-CSF) on H1N1 influenza virus infection was studied in vivo and in vitro. Mice were infected with H1N1 influenza A viruses and rHuGM-CSF at doses of 0.34, 0.67, and 1.34mgkg⁻¹d⁻¹ was administrated for 7days before the mice were infected with influenza virus and continued for a further 3days. Compared with control mice, rHuGM-CSF was demonstrated to increase the survival rate of the infected mice by 50.0%, 55.6%, and 80.0% and increased the mean survival days by 25.7%, 30.0%, and 46.8%, respectively. Histopathological study of the lungs in pneumonia mice found that pre-treatment with rHuGM-CSF significantly ameliorated lung injury induced by influenza virus infection. In vitro study demonstrated that when rHuGM-CSF were co-incubated with peripheral blood mononuclear cells (PBMCs), the PBMCs culture supernatant induced a dose-dependent reduction of virus-induced cytopathic effect (CPE) in Madin-Darby canine kidney (MDCK) cells in vitro. These results suggested that rHuGM-CSF might be an effective and potential protection for H1N1 influenza virus-induced pneumonia.