Abstract: The conditions of agar diffusion technique determining Nisin potency were studied.The accuracy andsensitivity of measure can be judged with the standard line’s slope and y intercept .The results showed that whenthe assay medium No lwas used.the suspension concentration of Micrococcus lysodeibticus was 107 cfu/ml,the agarconcentration was 0.75% .the thickness of agar layer was 2mm,we can obtain greater accuracy and sensitivity.Theaddition of Tween 20 made the accuracy reduce slightly.

Key words: Nisin Potency Agar diffusion technique Accuracy Sensitivity