The activity of lysozyme (EC 3.2.1.17), as one of the immune system components of silkworm Bombyx mori L., was determined in the cell-free hemolymph of fifth larval instar by the lyso- plate assay using Micrococcus lysodeikticus. The lysozyme activity of the beginning newly larvae was 39 μg/ml, then increased to 248 μg/ml of hemolymph in mature larvae. The injection of Staphylococcus aureus and Escherichia coli into larvae resulted in an increase in lysozyme activity within 24 hours to 274 and 328 μg/ml, respectively. Antioxidant enzymes, including catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), and ascorbate peroxidase (EC 1.11.1.11) have been detected also in hemolymph using isoenzyme native-polyacrylamide gel electrophoresis. The activities of catalase and ascorbate peroxidase isoenzymes were increased with time progress, especially at the wonder stage while, a slight increase in peroxidase activity was observed.