A technology of foam fractionation coupled with isoelectric precipitation was developed for effectively recovering casein from its highly diluted solution without using any surfactants as stabilizers due to its poor surface activity. The results showed that foam stability could be improved by using the pore diameter of gas distributor 125 gm and increasing the liquid phase height to 1750 mm. In the two-stage continuous foam fractionation, the enrichment ratio and the recovery percentage of casein were obtained as high as 12.1 and 92.3%, respectively. Then, the foamate was treated by precipitation and the supernatant could be used as the feed solution of the first stage foam fractionation. By using the coupled technology, the enrichment ratio was further increased to 52.6 and the recovery percentage was 91.7%. The concentration of casein 0.01 g/L and its mass percent 5% were got in the residual solution and the precipitated solution, respectively. (C) 2017 Published by Elsevier Ltd.