Recent research suggests hemocyanin acts as an immunologically multi-functional protein in invertebrates. However, little is known about the antibacterial activity of hemocyanin. We evaluated the antibacterial activity of this hemocyanin and its binding target to pathogens using antibacterial and antibacterial inhibition assays. The hemocyanin exhibited antibacterial activity against K12. This activity was completely or partly inhibited by the outer membrane proteins of hemocyanin against K12 Omp-deletion mutants of OmpW was significantly lower than that of the control. Together, our results suggest that hemocyanin exhibits antibacterial activity by binding to a range of outer membrane proteins