Src, a proto-oncogene, has been strongly implicated in the growth, progression and metastasis of a number of human cancers. Its role in lung cancer is, however, still unknown. In the present study, we assessed the expression of Src in three different human lung adenocarcinoma cell lines (PC-9, PC14PE6, A549), and explored the effect of a novel Src kinase inhibitor, M475271, on the behavior of the cell lines. The three cell lines expressed various levels of auto-phosphorylated Src. While M475271 reduced Src-phosphorylation and invasiveness of all three cell lines, it inhibited the proliferation of PC-9 and A549 cells with highly phosphorylated Src, but not PC14PE6 cells. We further examined the effect of M475271 on subcutaneous tumors and lung metastasis caused by PC-9 and/or A549 cells in NK-cell depleted SCID mice. Daily oral treatment with M475271 inhibited the growth of subcutaneous tumors with PC-9 and A549 cells via inhibition of tumor cells proliferation, VEGF production and/or vascularization in the mice in a dose-dependent manner. In the metastasis model with A549 cells, the lung weight in the M475271 (50 mg/kg)-treated group was less than that of the control group, despite no difference in the number of metastatic nodules. Our results suggest that inhibition of tyrosine kinase Src by M475271 could reduce the growth, invasion and VEGF-mediated neovascularization of lung adenocarcinoma cells, resulting in inhibition of growth of subcutaneous tumors and lung metastasis. Therefore, a novel Src tyrosine kinase inhibitor, M475271, might be helpful for controlling the progression of human lung adenocarcinoma.