The inhibitory effect of D- and DD-fragments and their mixture on plasma blood coagulation process under the action of thrombin has been studied. The significant increase of total efficiency of the inhibitory action has been shown. The inhibitors have influence on a lag-phase and lateral association of protofibrills of fibrin polymerization carried out by turbidimetry method in the model systems in vitro. The concentration of fragments which are close to parameters of fibrinogen/fibrin degradation products in pathological conditions was used. It is shown, that the covalent cross-link of D-dimer gamma-gamma-chains affects the inhibitory features and mechanism of interaction with fibrin monomer molecules. D-fragments inhibit the both phases of polymerization, whereas DD-fragments effectively inhibit the lateral association of protofibrill.