Ni0.5Zn0.5Fe2O4 nanoparticles were synthesized by the facile citrate-gel process and the preliminary measurement for adsorption of bovine serum albumin (BSA) protein on these nanoparticles was carried out. The gel precursor and resultant nanoparticles were characterized by TG-DSC. FTIR, XRD, TEM and VSM techniques and the BSA adsorption on the nanoparticles was analyzed by UV spectrophotometer at room temperature. The results show that the single phase of spinel Ni0.5Zn0.5Fe2O4 is formed at 400 degrees C. With increasing calcination temperature from 400 to 700 degrees C, the average grain size increases from about 14 to 45 nm and consequently, the specific saturation magnetization of Ni0.5Zn0.5Fe2O4 nanoparticles increases from about 46 to 68 Am-2/kg. The coercivity initially increases and then decreases with increasing calcination temperature, with a maximum value 9.2 kA/m at 500 degrees C. The as-prepared Ni0.5Zn0.5Fe2O4 nanoparticles exhibit a good adsorbing ability for BSA and the optimized adsorption is achieved for the Ni0.5Zn0.5Fe2O4 nanoparticles calcined at 500 degrees C with grain size about 24 nm. (C) 2011 Elsevier B.V. All rights reserved.