A protein designated Hypotin, with both antifungal and antibacterial activity, was isolated from peanut (Arachis hypogaea) seeds. The isolation procedure included extraction, ammonium sulfate precipitation, affinity chromatography on Affi-gel blue gel, ion chromatography, and gel filtration. The protein exhibited a molecular mass of 30.4 kDa in SDS-polyacrylamide gel electrophoresis under both reducing and nonreducing conditions, indicating that it is a monomeric protein. Its N-terminal sequence was highly homologous to those of chitinases and chitinase precursors from plants. It exerted potent antifungal action toward a variety of fungal species, including Pythium aphanidermatum, Fusarium solani, Physalospora piricola, Alternaria alternata, Botrytis cinerea, and Fusarium oxysporum. In addition, this novel protein exhibited antiproliferative activity against tumor cells. These findings further the progress in the research of leguminous plants.