A magnetic fluid was prepared by an oxidization-precipitation with FeCl2 and H2O2 in polyvinyl alcohol (PVA) solution. Cross-linked directly with glutaraldehyde, a magnetic support with magnetic particles entrapped by cross-linked PVA gel was produced. Cibacron blue 3GA (CB) was immobilized to the magnetic support to prepare the magnetic affinity support (MAS). The MAS was characterized by transmission electron microscopy (TEM) and infrared spectrum analysis. The TEM showed that the MAS ranged from 1 to 10 mum and consisted of nanometer-sized colloidal magnetite particles. It was determined that the MAS had a saturation magnetization of 1.16 x 10(3) A/m and showed no hysteresis in an external magnetic field of up to 5.6 x 10(5) A/m. The adsorption kinetics and equilibrium of bovine serum albumin (BSA) confirmed rapid adsorption and large capacity of the MAS. BSA adsorption reached equilibrium in 5 min. At a CB coupling density of 23 mu mol/g, the adsorption capacity of the MAS was 35 mg/g at an aqueous phase concentration of 0.1 mg/mL. The possibility of repetitive uses of the MAS was also demonstrated, indicating the stability of the magnetic support for protein adsorption.