Recent studies suggest that lysozyme, rich in hen egg, has an antitumor function. In the present study, we investigated the antitumor and antiangiogenesis effects of a newly isolated marine lysozyme both in vitro and in vivo. First, we showed that this marine-derived lysozyme specifically inhibits the proliferation of endothelial cells (ECV304) in a dose-dependent manner with no cytotoxicity (IC50=3.64 mu M). Second, we showed that this marine lysozyme directly suppresses neovascularization in chicken embryos using chorioallantoic membrane assay. Third, we demonstrated that this marine lysozyme markedly inhibits tumor growth in mice bearing either sarcoma 180 or hepatoma 22. Unexpectedly, hen egg lysozyme has no effects on the proliferation of endothelial cells in vitro or neovascularization in chicken embryos or tumor growth in nude mice at the same dosage range. Taken together, our studies clearly show that the newly identified marine lysozyme is a potent antitumor molecule, which may inhibit tumor growth and inhibit angiogenesis. We believe that this marine lysozyme may have a therapeutic value in antitumor drug development.