Magnetic investigation of spinel ferrite nanoparticles dispersed in biocompatible polymeric microspheres is reported in this study. X-ray diffraction data analysis confirms the presence of nanosized CoFe2 04 particles (mean size of ∼ 8 nm). This finding is corroborated by transmission electron microscopy micrographs. Magnetization isotherms suggest a spin disorder likely occurring at the nanoparticle's surface. The saturation magnetization value is used to estimate particle concentration of 1.6 × 1018 cm-3 dispersed in the polymeric template. A T 1/2 dependence of the coercive field is determined in the low-temperature region (T < 30 K). The model of non-interacting mono-domains is used to estimate an effective magnetic anisotropy of Keff = 0.6 × 105 J/m3. The Keff value we found is lower than the value reported for spherically-shaped CoFe2 O 4 nanoparticles, though consistent with the low coercive field observed in the investigated sample. © 2009 IEEE.