BACKGROUND Superparamagnetic iron oxide nanoparticles (SPIONs) are inorganic nanomaterials gaining strong clinical interest due to their increasing number of biological and medical applications. The stabilization of SPIONs in a biocompatible stable suspension (bioferrofluid) is generally achieved by an adequate polymeric coating. As many applications using these materials are intended for clinical use through intravenous injection, it is of outmost importance to evaluate their hemostatic behaviour. OBJECTIVE The aim of this work is to evaluate the hemocompatibility of selected polymer coated bioferrofluids and of their separated components by observing the effects of the bioferrofluid on: the coagulation process--by measuring the prothrombin time (PT) and activated partial thromboplastin time (aPTT)--, the complete blood count (CBC)--Erythrocytes, Leucocytes, Platelets, Hemoglobin and hematocrit--and the hemolysis. METHODS A SPIONs/bioferrofluid model consisting of a magnetic core of iron oxide nanoparticles embedded within poly(4-vinyl pyridine) (P4VP) and all coated with polyethylene glycol (PEG) has been selected. CONCLUSIONS By increasing the concentration of the bioferrofluids an inhibitory effect on the intrinsic pathway of blood coagulation is observed, as indicated by significant increase in aPTT in vitro while PT values stay normal. The effect of the coating components on the inhibition of blood coagulation process shows that PEG has no effect on the process while the P4VP-g-PEG copolymer coating has a strong anticoagulant effect indicating that P4VP is at the origin of such effects. The studied bioferrofluids have no effect on the CBC neither they show in vitro hemolytic effect on blood.