When nanoparticles enter a living organism, it is very likely they will appear in the bloodstream, which raises the question of the hemocompatibility of various nanomaterials. The effect of carbon nanoparticles (shungite nanocarbon and nanodiamonds) on the human and mink blood coagulation system in vitro was studied. The time of plasma clotting triggered by recalcification was used as a test parameter for assessing the state of the internal coagulation system activation pathways. The effect of shungite nanocarbon at 3 to 6 μg/ml concentrations on the activity of the human coagulation system manifest itself in a significant decrease in the recalcification time. When carbon nanoparticles were added to the mink plasma, a significant decrease in the recalcification time was observed starting at a concentration of 6 μg/ml. The presence of nanodiamonds in the 9 μg/ml concentration significantly accelerated the formation of a human plasma clot. We suppose that hypercoagulation in the presence of shungite carbon and nanodiamonds can be associated with a faster fibrin polymerization. This may be a result of fibrin interaction with shungite carbon nanoparticles and nanodiamonds, which can thus induce platelet activation and/or aggregation. The molecular mechanism behind the revealed thrombogenicity of carbon nanoparticles is discussed.