Abstract: Five different effective microorganisms (EM) were studied for their antimicrobial activity against various pathogenic bacteria in vitro. Type EM3, EM4 and EM5 showed good antibacterial activity against animal pathogens including Escherichia coli, Salmonella spp., Pasteurella spp. and Staphylococcus spp. There was an inverse correlation between the antibacterial and the higher dilution of the culture. All biologically active EM5, may be used efficiently at the highest dilution of 104, while the EM2 and EM3 proved ineffective against the pathogenic organisms under study.