Insects are a large, unexplored and unexploited source of potentially useful compounds for modern medicine. In many insects, lectins present in the haemolymph and play important roles in internal host defense mechanisms. The objective of this study was to evaluate the antibacterial and mitogenic activity of Musca domestica pupae lectin (MPL).The main fraction of lectin in buffer insect solution (BIS) was purified by affinity chromatography on D-galactose-Sepharose-4B and ultrafiltration. MPL agglutinated typsin treated rabbit blood cells (RBC) and such hemagglutination activity was inhibited by D-galactose. MPL showed strong broad spectrum antibacterial activity against both gram-negative and gram-positive, while gram-negative bacteria were more resistant than gram-positive bacteria. The purified MPL mediate agglutination of the tested bacteria, thereby indicating a possible mode of action in physiological situation. The lectin further showed mitogenic activity to mouse splenocytes. Our results suggested the lectin of M. domestica involves the defense of body against microbial invasion and stimulates splenocytes proliferation.