Nisin is a 34-residue peptide and it is widely used as food preservative. Different strategies for nisin purification from the complex broth have been investigated. But these methods increase the cost of nisin production, and its wide application is limited. Foam separation is an economical and effective technology for protein concentration and separation. In this paper, we utilized foam separation technology to recover nisin from fermentation broth, and studied the effect of ionic strength on the experimental system. The results showed that with ionic strength increasing, surface tension and inactivation ratio first decreased and then increased, and, however, foaming ability, foam stability, enrichment ratio and recovery first increased and then decreased. Under the conditions of the titer of nisin fermentation broth 4200 IU/ml, pH 3.0, feed liquid 250 ml, air flow rate 30 ml/min and temperature 25 degrees C. the maximum enrichment ratio and recovery and the minimum inactivation ratio of nisin reached 6.4, 86.44% and 9.89%, respectively, when the ionic strength was 0.41 mol/kg. Furthermore, we obtained higher nisin recovery and activity using sodium rather than potassium salt. (c) 2011 Elsevier B.V. All rights reserved.