Objective To examine whether IFN-λ has the ability to inhibit HIV-1 infection of blood monocyte-derived macrophages and its mechanism(s). Methods Macrophages were pretreated with IFN-λ/ IFN-λ2 for 24 h before infected by HIV-1 R5 strains (Bal, Jago, and JRFL). And then the culture supernatants were detected HIV-1 reverse transcription (RT) activity and p24 protein expression by HIV-1 BT assay and ELISA. The expressions of IFN-λ receptor, CD4, CCRS, CXCR4 were evaluated by real-time PCR. Results Both IFN-λ1 and IFN-λ2, when added to macrophage cultures, inhibited HIV-1 infection and replication. This IFN-λ-mediated anti-HIV-I activity is broad, as IFN-λ could inhibit infection by both laboratory-adapted and clinical strains of HIV-1. Investigations of mechanism(s) responsible for the IFN-λ action showed that although IFN-λ had little effect on HIV-1 entry receptor CD4 and co-receptor CCR5 and CXCR4 expression, IFN-λ inhibited HIV-I infection of macrophages through connecting with IFN-λ recep-tor. Conclusion IFN-λ could inhibit HIV-I replication in macrophages. These findings indicate that IFN-λ may have a therapeutic value in the treatment of HIV-1 infection.