Abstract: By injection of Escherichia coli K₁₂D₃₁ into 6th instar larvae of Spodoptera litura , antibacterial substances were induced in haemolymph of the larvae after 12 h. SDS-PAGE analysis indicated that there were three bands with molecular weight 43.5 , 15.0 and 4.0 kD , respectively , in the antibacterial crude extract. Characterization of the antibacterial substances showed that the induced antibacterial substances kept high stability under acid condition , a short-time exposure to heating and room temperature. The an-tibacterial substances were also inhibitive to Candida albicans and Saceharomyces cerevisiae , besides Salmonella choleraesuis subsp. choleraesuis , Bacillus subtilis and Pseudomonas aeruginosa , and other bacteria.