Magnetic Co3 O4 nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co3 O4 NPs were prepared via sol-gel method and encapsulated with a layer of TiO2 , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co3 O4 spinel with TiO2 . The Co3 O4 cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO2 . According to the neutral red uptake assay, the coating of the cores with TiO2 significantly decreases the cytotoxic character of the Co3 O4 particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co3 O4 @TiO2 core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.