In this study, gas-assisted superparamagnetic extraction (GASE) with potential large-scale application was proposed for selective separation of multicomponent proteins. Magnetic poly(glycidyl methacrylate)-iminodiacetic acid Zn2+ microspheres (MPMs) for selective separation of bovine serum albumin (BSA) and bovine hemoglobin (BHb) are selected as a model. The feasibility of flotation for concentrating BHb-loaded MPMs from dilute mixed proteins solution was proved. The well-concentrated solution of BHb-loaded MPMs could be achieved by simple adjustment of pH values and ionic strength in low regions, without additive detergent. Impurity BSA had the effects of improving the flotability of BHb-loaded MPMs, acting as foaming agent, but decreasing the enrichment ratio in the GASE process. The flotation conditions and the selective adsorption ones showed strong consistency. Under the optimal conditions, the enrichment ratio of 39 and recovery percentage of 98% was obtained within 1.3 min. Furthermore, the enrichment ratio could be further improved by added flotation steps.