Meatborne listeriosis because of Listeria monocytogenes in ground beef in many countries is most serious problem in the last years. The effect of various concentrations of commercially nisin on Listeria monocytogenes in tryptose phoshate broth and then in ground beef at refrigerated temperature were investigated. The inoculated numbers of Listeria monocytogenes was 9x10* CFU/ml and 5. 2x10° CFU/g for tryptose phoshate broth and ground beef respectively. The used concentrations of nisin were 800, 1600 and 2400 RU for this purpose. The effect of nisin on Listeria monocytogenes was varied according to its concentration and the substance involved. Its effect on ground beef was differ from that in tryptose phoshate broth due to the competitive flora in ground beef. The use of 2400 RU nisin to inactivate Listeria monocytogenes at refrigerator temperature was recommended.