koumiss, a traditional and national dairy product in the Inner Mongolia, was researched.The antibiotic factors were preliminarily isolated from koumiss. Its antibiotic activity was detected by cylinder-plate method,which is similar to the determination of antibiotic liter. In order to get the best inhibitory effect on bacteria, Some factors that affected determination were analyzed. Many factors including density of the target strains, concentration of agar, culture time, thickness of the medium...