Objective: The lowest concentration of sodium dodecyl sulfate (SOS) separated capably from its feed solution using a one-stage foam separation was determined. Both enrichment ratio and recovery percentage of SOS were increased and SDS concentration of the residual solution was decreased at its lowest concentration. Materials method: The effects of SOS concentration and superficial gas velocity on foaming height and enrichment ratio of SDS were studied in order to determine the lowest SDS concentration in foam separation. A two-stage foam separation technology using only one column was developed to improve the performances at the lowest SOS concentration. Results: The results showed that the lowest SDS concentration in foam separation was 50 mg/L. In the one-stage foam separation, SOS surface excess increased with increasing the height of the liquid phase and the pore diameter of gas distributor, thus enrichment ratio increased from 1.9 to 7.2 and however, recovery percentage decreased and SDS concentration of the residual solution significantly increased. In the developed two-stage foam separation, enrichment ratio and recovery percentage increased to 28.0 and 94.2%, respectively and at the same time, SOS concentration of the residual solution decreased to 6.0 mg/L under the operating conditions of SOS concentration of the feed solution of 50.0 mg/L, loading volume of 0.630 L and superficial gas velocity of 1.33 mm/s. (C) 2014 Elsevier B.V. All rights reserved.