Plant ribosome-inactivating proteins (RIPs) have multiple biological functions, and have been widely used in the studies on biomedical and agronomic applications. Moschatin is a novel single-chain RIP recently purified from pumpkin seeds, and it has been successfully applied to construct the immunotoxin that can selectively kill the cultured human melanoma cells. Six stable strains of hybridomas (2H8, 4A8, 5B6, 6F8, 4H10 and 6C2) that can secrete high specific monoclonal antibodies against Moschatin have been successfully prepared using hybridoma technique. The isotypes of these monoclonal antibodies are IgG1, IgG1, IgG1, IgG1, IgG2a and IgGM. Their affinity constants were determined to be 1.42x10(8), 2.71x10(8), 8.72x10(7), 2.06x10(8), 1.36x10(8) and 1.51x10(8) M(-1) in a sequent order, measured by non-competitive ELISA. The monoclonal antibody 4A8 has been used to detect Moschatin in Western blot. An immunoaffinity gel, which consisted of a monoclonal antibody 4H10 and Sepharose 4B, was prepared and used to purify Moschatin from pumpkin seeds crude extract.