The peak of anti\|bacterial activity in 3rd larvae IH of \%Musca domestica\% L.pricked with No.3 insect needle being treated with E.coil K\-\{12\}D\-\{31\} appears at 36-48h after induction. The anti-bacterial substance is weakly alkaline and heat-stable(100℃)and cold\|tolerant(-40℃).The result of capillary zone electrophoresis shows that there is no apparent difference between ck and IH, which suggested that the anti\|bacterial substances of \%Musca domestica\% L. might be regulated by the host structural genes.