In this study, we investigated the Bovine Serum Albumin (BSA) protein affinity for manufactured metal oxide nanoparticles (NPs), respectively TiO2 and CeO2. Changes in the NPs surface charge property and resulting stability were investigated by considering pH-dependent electrostatic scenarios and contrasting solution conditions from ultra-pure water to more complex biological mixtures regarding the ionic and protein composition. After careful characterization of NPs and BSA as a function of pH, we used variable BSA concentrations to study the impact of BSA adsorption and we found that protein affinity for NPs was largely controlled by electrostatic interactions. We demonstrated that in ultra-pure water increasing gradually the BSA concentration results in aggregation when BSA and NPs charges are opposite (charge neutralization). On the other hand, when NPs were added in a solution containing BSA, aggregation was prevented due to corona formation. Then, the ultrapure water was replaced by Dulbecco's phosphate-buffered saline (DPBS) to mimic the blood composition and ionic strength. BSA was then replaced by fetal calf serum (FCS) to mimic the great variety of proteins and other biomolecules found in the blood. Our findings indicate that, in all cases, initially dispersed TiO2 or CeO2 NPs are stabilized by the presence of proteins and that protein adsorption is fast regarding NPs homoaggregation. Proteins are found to improve NPs dispersion even at high ionic strength with overarching consequences on the fate, transport and related risk of NPs in living systems.