The natural silk sericin recovered from Bombyx mori silk waste by the degumming processing in the high-temperature and high-pressure is a macromolecular protein. Amino acid composition and molecular weight range of the sericin protein as a vector for enzyme immobilization were investigated. The silk sericin protein with different molecular mass from 50 to 200kDa was poorly soluble microparticles with an average size of about 10μm. Anti-leukemic enzyme l-asparaginase (l-ASNase) was covalently conjugated on the microparticles of the sericin protein. The immobilized l-ASNase on the natural support by cross-linking with glutaraldehyde maintained 62.5% of the original activity of the enzyme. The K m of sericin-conjugates was 8 times lower than that of native l-ASNase. The bioconjugation of l-ASNase widened the optimum reactive temperature range of the enzyme. The immobilized l-ASNase showed significantly higher stability when the temperature raised to 40-50 o C, it also showed preferable resistance to trypsin digestion as compared with native enzyme. The results are discussed regarding the possible explanations of sericin-induced enzyme stability, as well as the possible applications of immobilized l-ASNase research.