The biocompatibility of carrier nanomaterials in blood is largely hampered by their activating or inhibiting role on the clotting system, which in many cases prevents safe intravascular application. Here, we characterized an aqueous colloidal ethyl hydroxyethyl cellulose (EHEC) solution and tested its effect on ex vivo clot formation, platelet aggregation, and activation by thromboelastometry, aggregometry, and flow cytometry. We compared the impact of EHEC solution on platelet aggregation with biocompatible materials used in transfusion medicine (the plasma expanders gelatin polysuccinate and hydroxyethyl starch). We demonstrate that the EHEC solution, in contrast to commercial products exhibiting Newtonian flow behavior, resembles the shear-thinning behavior of human blood. Similar to established nanomaterials that are considered biocompatible when added to blood, the EHEC exposure of resting platelets in platelet-rich plasma does not enhance tissue thromboplastin- or ellagic acid-induced blood clotting, or platelet aggregation or activation, as measured by integrin α_IIbβ₃ activation and P-selectin exposure. Furthermore, the addition of EHEC solution to adenosine diphosphate (ADP)-stimulated platelet-rich plasma does not affect the platelet aggregation induced by this agonist. Overall, our results suggest that EHEC may be suitable as a biocompatible carrier material in blood circulation and for applications in flow-dependent diagnostics.