Monodisperse core-shell hybrid nanoparticles based on cobalt ferrite (CoFe2O4) particles coated with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) biopolymers were obtained employing a two-step procedure: the CoFe2O4 of 21 nm mean particle size were first synthesized by coprecipitation method assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The FTIR spectra also indicated the interaction between the cobalt ferrite particles and the two polymers were used as bio-compatible coatings. Transmission electron microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses revealed the formation of approximately 22 nm CoFe2O4-PVP and CoFe2O4-PEG hybrid nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids on Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica serovar typhimurium bacteria and Candida scotti yeast it was clear that no significant toxic activity was obtained. Moreover, all the prepared nanohybrids and their components possess antioxidant activity. (C) 2012 Elsevier B.V. All rights reserved.