Abstract Type III interferon (IFN-λ) is a novel member of the interferon family, which preferentially promotes antiviral responses from epithelial cells and cooperates with type I IFNs in the clearance of viral infections. However, the effect of mIFN-λ2 to the LA795 lung adenocarcinoma cell is largely unknown. In this study, we transfected Ad-mIFN-λ2 vector into LA795 tumor-bearing mice to explore the effect of mIFN-λ2 on the proliferation of LA795 lung adenocarcinoma cell and on the immune response of the mice. Transfected by Ad-mIFN-λ2 vector, a significant decrease in the tumor growth, the subcutaneous tumor necrosis, cystic degeneration, and tumor apoptosis were more evident; at the same time, mIFN-λ2 protein and gene were significantly more expressed. And, flow cytometry analysis suggested that CD3(+)CD4(+), CD3(+)CD8(+), and NK (CD3(-)CD49(+)) cells were all significantly increased after transfected by Ad-mIFN-λ2. The study demonstrated that recombinant Ad-mIFN-λ2 transfection effectively inhibited the growth of LA795 lung adenocarcinoma cell, which may work through inducing apoptosis of tumor cell and regulating cell immune response.